C Programming Tutorial for Beginners: Complete 50-Hour Guide from Scratch

#include <stdio.h>

int main() {
    printf("Hello World!");
    return 0;
}

#include <stdio.h>

int main() {
    printf("Hello World!\n");
    printf("Welcome to C Programming!");
    return 0;
}

#include <stdio.h>

int main() {
    printf("Hello World!\nWelcome to C Programming!\nLet's start learning!");
    return 0;
}

#include <stdio.h>

int main() {
    printf("My name is John\n");
    printf("I am 20 years old");
    return 0;
}

#include <stdio.h>

int main() {
    printf("=== MAIN MENU ===\n");
    printf("1. Start Game\n");
    printf("2. Settings\n");
    printf("3. Exit");
    return 0;
}

#include <stdio.h>

int main() {
    int age;           // Declare an integer variable
    float height;      // Declare a float variable
    char grade;        // Declare a character variable
    
    age = 20;          // Assign value to age
    height = 5.8;      // Assign value to height
    grade = 'A';       // Assign value to grade
    
    printf("Age: %d\n", age);
    printf("Height: %.1f feet\n", height);
    printf("Grade: %c\n", grade);
    
    return 0;
}

#include <stdio.h>

int main() {
    // Declare and initialize in one line
    int students = 30;
    float price = 99.99;
    char initial = 'J';
    
    printf("Number of students: %d\n", students);
    printf("Price: Rs.%.2f\n", price);
    printf("First initial: %c\n", initial);
    
    return 0;
}

#include <stdio.h>

int main() {
    const float PI = 3.14159;
    const int DAYS_IN_WEEK = 7;
    
    printf("Value of PI: %.5f\n", PI);
    printf("Days in a week: %d\n", DAYS_IN_WEEK);
    
    // PI = 3.14;  // This would cause an error!
    
    return 0;
}

#include <stdio.h>
#define MAX_STUDENTS 50
#define SCHOOL_NAME "ABC High School"

int main() {
    printf("School: %s\n", SCHOOL_NAME);
    printf("Maximum students allowed: %d\n", MAX_STUDENTS);
    
    return 0;
}

#include <stdio.h>

int main() {
    char title_initial = 'H';
    int pages = 350;
    float price = 29.99;
    
    printf("Book title starts with: %c\n", title_initial);
    printf("Number of pages: %d\n", pages);
    printf("Price: $%.2f\n", price);
    
    return 0;
}

#include <stdio.h>

int main() {
    float length = 10.5;
    float width = 6.2;
    float area;
    
    area = length * width;
    
    printf("Length: %.1f meters\n", length);
    printf("Width: %.1f meters\n", width);
    printf("Area: %.2f square meters\n", area);
    
    return 0;
}

#include <stdio.h>

int main() {
    int a = 15;
    int b = 4;
    
    printf("a = %d, b = %d\n", a, b);
    printf("a + b = %d\n", a + b);
    printf("a - b = %d\n", a - b);
    printf("a * b = %d\n", a * b);
    printf("a / b = %d\n", a / b);        // Integer division
    printf("a %% b = %d\n", a % b);       // Remainder
    
    return 0;
}

#include <stdio.h>

int main() {
    float x = 15.0;
    float y = 4.0;
    int count = 5;
    
    printf("Float division: %.2f / %.2f = %.2f\n", x, y, x/y);
    
    printf("Original count: %d\n", count);
    count++;  // Increment by 1
    printf("After increment: %d\n", count);
    count--;  // Decrement by 1
    printf("After decrement: %d\n", count);

    return 0;
}

#include <stdio.h>

int main() {
    int x = 10;
    int y = 20;
    
    printf("x = %d, y = %d\n", x, y);
    printf("x == y: %d\n", x == y);    // False = 0
    printf("x != y: %d\n", x != y);    // True = 1
    printf("x > y: %d\n", x > y);      // False = 0
    printf("x < y: %d\n", x < y);      // True = 1
    printf("x >= y: %d\n", x >= y);    // False = 0
    printf("x <= y: %d\n", x <= y);    // True = 1
    
    return 0;
}

#include <stdio.h>

int main() {
    int age = 25;
    int income = 30000;
    
    printf("Age: %d, Income: %d\n", age, income);
    
    // AND operator
    printf("Eligible for loan (age >= 18 AND income >= 25000): %d\n", 
           (age >= 18) && (income >= 25000));
    
    // OR operator
    printf("Special discount (age < 18 OR age > 60): %d\n", 
           (age < 18) || (age > 60));
    
    // NOT operator
    printf("Not a senior citizen (age < 65): %d\n", !(age >= 65));
    
    return 0;
}

#include <stdio.h>

int main() {
    int num = 10;
    
    printf("Initial value: %d\n", num);
    
    num += 5;    // num = num + 5
    printf("After += 5: %d\n", num);
    
    num -= 3;    // num = num - 3
    printf("After -= 3: %d\n", num);
    
    num *= 2;    // num = num * 2
    printf("After *= 2: %d\n", num);
    
    num /= 4;    // num = num / 4
    printf("After /= 4: %d\n", num);
    
    num %= 3;    // num = num % 3
    printf("After %= 3: %d\n", num);
    
    return 0;
}

#include <stdio.h>

int main() {
    float num1 = 85.5;
    float num2 = 92.0;
    float num3 = 78.5;
    float average;
    
    average = (num1 + num2 + num3) / 3;
    
    printf("Number 1: %.1f\n", num1);
    printf("Number 2: %.1f\n", num2);
    printf("Number 3: %.1f\n", num3);
    printf("Average: %.2f\n", average);
    
    return 0;
}

#include <stdio.h>

int main() {
    int number = 17;
    int remainder;
    
    remainder = number % 2;
    
    printf("Number: %d\n", number);
    printf("Remainder when divided by 2: %d\n", remainder);
    
    if (remainder == 0) {
        printf("The number is EVEN\n");
    } else {
        printf("The number is ODD\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int age = 25;
    float height = 5.9;
    char grade = 'A';
    
    printf("Age: %d years\n", age);
    printf("Height: %.1f feet\n", height);
    printf("Grade: %c\n", grade);
    printf("Height with 3 decimals: %.3f\n", height);
    
    return 0;
}

#include <stdio.h>

int main() {
    int age;
    float salary;
    char grade;
    
    printf("Enter your age: ");
    scanf("%d", &age);
    
    printf("Enter your salary: ");
    scanf("%f", &salary);
    
    printf("Enter your grade: ");
    scanf(" %c", &grade);  // Note the space before %c
    
    printf("\n--- Your Information ---\n");
    printf("Age: %d years\n", age);
    printf("Salary: $%.2f\n", salary);
    printf("Grade: %c\n", grade);
    
    return 0;

}

#include <stdio.h>

int main() {
    int day, month, year;
    
    printf("Enter date (DD MM YYYY): ");
    scanf("%d %d %d", &day, &month, &year);
    
    printf("You entered: %02d/%02d/%d\n", day, month, year);
    // %02d means: 2 digits, fill with 0 if needed
    
    return 0;
}

#include <stdio.h>

int main() {
    char name[50];  // Array to store string
    int age;
    
    printf("Enter your name: ");
    scanf("%s", name);  // No & needed for strings
    
    printf("Enter your age: ");
    scanf("%d", &age);
    
    printf("Hello %s, you are %d years old!\n", name, age);
    
    return 0;
}

#include <stdio.h>

int main() {
    float num1, num2, result;
    char operator;
    
    printf("=== Simple Calculator ===\n");
    printf("Enter first number: ");
    scanf("%f", &num1);
    
    printf("Enter operator (+, -, *, /): ");
    scanf(" %c", &operator);
    
    printf("Enter second number: ");
    scanf("%f", &num2);
    
    // Perform calculation based on operator
    if (operator == '+') {
        result = num1 + num2;
    } else if (operator == '-') {
        result = num1 - num2;
    } else if (operator == '*') {
        result = num1 * num2;
    } else if (operator == '/') {
        result = num1 / num2;
    }
    
    printf("%.2f %c %.2f = %.2f\n", num1, operator, num2, result);
    
    return 0;
}

// Wrong way
scanf("%d", &num);
scanf("%c", &ch);  // This might not work correctly

// Correct way
scanf("%d", &num);
scanf(" %c", &ch);  // Note the space before %c

// scanf() stops at spaces
scanf("%s", name);  // Input: "John Smith" → Only gets "John"

// Solution: Use gets() or fgets()
gets(name);  // Gets entire line including spaces

#include <stdio.h>

int main() {
    char name[50];
    int age;
    int fav_number;
    
    printf("Enter your name: ");
    scanf("%s", name);
    
    printf("Enter your age: ");
    scanf("%d", &age);
    
    printf("Enter your favorite number: ");
    scanf("%d", &fav_number);
    
    printf("\n=== Your Profile ===\n");
    printf("Name: %s\n", name);
    printf("Age: %d years old\n", age);
    printf("Favorite Number: %d\n", fav_number);
    
    return 0;
}

#include <stdio.h>

int main() {
    float length, width, area, perimeter;
    
    printf("Enter rectangle length: ");
    scanf("%f", &length);
    
    printf("Enter rectangle width: ");
    scanf("%f", &width);
    
    area = length * width;
    perimeter = 2 * (length + width);
    
    printf("\n=== Rectangle Information ===\n");
    printf("Length: %.2f units\n", length);
    printf("Width: %.2f units\n", width);
    printf("Area: %.2f square units\n", area);
    printf("Perimeter: %.2f units\n", perimeter);
    
    return 0;
}

if (condition) {    
		// Code to execute if condition is true
}

#include <stdio.h>

int main() {
    int age;
    
    printf("Enter your age: ");
    scanf("%d", &age);
    
    if (age >= 18) {
        printf("You are eligible to vote!\n");
    }
    
    printf("Program ended.\n");
    
    return 0;
}

if (condition) {    
		// Code to execute if condition is true
}

#include <stdio.h>

int main() {
    int number;
    
    printf("Enter a number: ");
    scanf("%d", &number);
    
    if (number % 2 == 0) {
        printf("%d is an EVEN number.\n", number);
    } else {
        printf("%d is an ODD number.\n", number);
    }
    
    return 0;

}

if (condition1) {
    // Code for condition1
} else if (condition2) {
    // Code for condition2
} else if (condition3) {
    // Code for condition3
} else {
    // Code if none of the above conditions are true
}

#include <stdio.h>

int main() {
    int marks;
    
    printf("Enter your marks (0-100): ");
    scanf("%d", &marks);
    
    if (marks >= 90) {
        printf("Grade: A+ (Excellent!)\n");
    } else if (marks >= 80) {
        printf("Grade: A (Very Good!)\n");
    } else if (marks >= 70) {
        printf("Grade: B (Good!)\n");
    } else if (marks >= 60) {
        printf("Grade: C (Average)\n");
    } else if (marks >= 50) {
        printf("Grade: D (Pass)\n");
    } else {
        printf("Grade: F (Fail)\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int user_id;
    int password;
    int age;
    
    printf("Enter User ID: ");
    scanf("%d", &user_id);
    
    if (user_id == 1234) {
        printf("Enter Password: ");
        scanf("%d", &password);
        
        if (password == 9999) {
            printf("Enter your age: ");
            scanf("%d", &age);
            
            if (age >= 18) {
                printf("Access GRANTED! Welcome!\n");
            } else {
                printf("Access DENIED! Must be 18 or older.\n");
            }
        } else {
            printf("Wrong password!\n");
        }
    } else {
        printf("Invalid User ID!\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int age;
    int income;
    
    printf("Enter age: ");
    scanf("%d", &age);
    printf("Enter monthly income: ");
    scanf("%d", &income);
    
    if (age >= 21 && income >= 30000) {
        printf("You qualify for a premium credit card!\n");
    } else {
        printf("You don't qualify for premium credit card.\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int age;
    
    printf("Enter your age: ");
    scanf("%d", &age);
    
    if (age < 13 || age > 65) {
        printf("You get a special discount!\n");
    } else {
        printf("Regular price applies.\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int pin = 1234;           // Correct PIN
    int balance = 5000;       // Account balance
    int entered_pin;
    int withdraw_amount;
    
    printf("=== ATM System ===\n");
    printf("Enter your PIN: ");
    scanf("%d", &entered_pin);
    
    if (entered_pin == pin) {
        printf("PIN Correct!\n");
        printf("Current balance: $%d\n", balance);
        printf("Enter withdrawal amount: ");
        scanf("%d", &withdraw_amount);
        
        if (withdraw_amount > 0 && withdraw_amount <= balance) {
            balance = balance - withdraw_amount;
            printf("Transaction successful!\n");
            printf("Withdrawn: $%d\n", withdraw_amount);
            printf("Remaining balance: $%d\n", balance);
        } else if (withdraw_amount > balance) {
            printf("Insufficient funds!\n");
        } else {
            printf("Invalid amount!\n");
        }
    } else {
        printf("Wrong PIN! Access denied.\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    // Code goes here
    return 0;
}

switch (variable) {
    case value1:
        // Code for value1
        break;
    case value2:
        // Code for value2
        break;
    case value3:
        // Code for value3
        break;
    default:
        // Code if no cases match
}

#include <stdio.h>

int main() {
    int choice;
    
    printf("=== Main Menu ===\n");
    printf("1. Play Game\n");
    printf("2. View Settings\n");
    printf("3. View Help\n");
    printf("4. Exit\n");
    printf("Enter your choice (1-4): ");
    scanf("%d", &choice);
    
    switch (choice) {
        case 1:
            printf("Starting the game...\n");
            break;
        case 2:
            printf("Opening settings menu...\n");
            break;
        case 3:
            printf("Displaying help information...\n");
            break;
        case 4:
            printf("Thank you for playing! Goodbye!\n");
            break;
        default:
            printf("Invalid choice! Please enter 1-4.\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    float num1, num2, result;
    char operator;
    
    printf("=== Calculator ===\n");
    printf("Enter first number: ");
    scanf("%f", &num1);
    
    printf("Enter operator (+, -, *, /): ");
    scanf(" %c", &operator);
    
    printf("Enter second number: ");
    scanf("%f", &num2);
    
    switch (operator) {
        case '+':
            result = num1 + num2;
            printf("%.2f + %.2f = %.2f\n", num1, num2, result);
            break;
            
        case '-':
            result = num1 - num2;
            printf("%.2f - %.2f = %.2f\n", num1, num2, result);
            break;
            
        case '*':
            result = num1 * num2;
            printf("%.2f * %.2f = %.2f\n", num1, num2, result);
            break;
            
        case '/':
            if (num2 != 0) {
                result = num1 / num2;
                printf("%.2f / %.2f = %.2f\n", num1, num2, result);
            } else {
                printf("Error: Division by zero!\n");
            }
            break;
            
        default:
            printf("Error: Invalid operator!\n");
            printf("Please use +, -, *, or /\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    char grade;
    
    printf("Enter your grade (A, B, C, D, F): ");
    scanf(" %c", &grade);
    
    switch (grade) {
        case 'A':
        case 'a':  // Handle both uppercase and lowercase
            printf("Excellent! You scored 90-100%%\n");
            printf("Keep up the great work!\n");
            break;
            
        case 'B':
        case 'b':
            printf("Very Good! You scored 80-89%%\n");
            printf("You're doing well!\n");
            break;
            
        case 'C':
        case 'c':
            printf("Good! You scored 70-79%%\n");
            printf("There's room for improvement.\n");
            break;
            
        case 'D':
        case 'd':
            printf("Satisfactory. You scored 60-69%%\n");
            printf("You need to study harder.\n");
            break;
            
        case 'F':
        case 'f':
            printf("Fail. You scored below 60%%\n");
            printf("Don't give up! Try again.\n");
            break;
            
        default:
            printf("Invalid grade! Please enter A, B, C, D, or F.\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int day = 2;
    
    printf("Day %d: ", day);
    
    switch (day) {
        case 1:
            printf("Monday ");
        case 2:
            printf("Tuesday ");
        case 3:
            printf("Wednesday ");
        case 4:
            printf("Thursday ");
        case 5:
            printf("Friday ");
        default:
            printf("(Workday)\n");
    }
    
    return 0;
}

switch (day) {
    case 1:
        printf("Monday\n");
        break;
    case 2:
        printf("Tuesday\n");
        break;
    case 3:
        printf("Wednesday\n");
        break;
    // ... and so on
}

#include <stdio.h>

int main() {
    int month;
    
    printf("Enter month number (1-12): ");
    scanf("%d", &month);
    
    switch (month) {
        case 12:
        case 1:
        case 2:
            printf("Winter season\n");
            break;
            
        case 3:
        case 4:
        case 5:
            printf("Spring season\n");
            break;
            
        case 6:
        case 7:
        case 8:
            printf("Summer season\n");
            break;
            
        case 9:
        case 10:
        case 11:
            printf("Autumn season\n");
            break;
            
        default:
            printf("Invalid month! Enter 1-12.\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int choice;
    float balance = 1500.00;  // Starting balance
    float amount;
    
    printf("=== ATM Machine ===\n");
    printf("Current Balance: $%.2f\n\n", balance);
    printf("1. Check Balance\n");
    printf("2. Deposit Money\n");
    printf("3. Withdraw Money\n");
    printf("4. Exit\n");
    printf("Select an option: ");
    scanf("%d", &choice);
    
    switch (choice) {
        case 1:
            printf("\nYour current balance is: $%.2f\n", balance);
            break;
            
        case 2:
            printf("Enter deposit amount: $");
            scanf("%f", &amount);
            if (amount > 0) {
                balance += amount;
                printf("$%.2f deposited successfully!\n", amount);
                printf("New balance: $%.2f\n", balance);
            } else {
                printf("Invalid amount!\n");
            }
            break;
            
        case 3:
            printf("Enter withdrawal amount: $");
            scanf("%f", &amount);
            if (amount > 0 && amount <= balance) {
                balance -= amount;
                printf("$%.2f withdrawn successfully!\n", amount);
                printf("Remaining balance: $%.2f\n", balance);
            } else if (amount > balance) {
                printf("Insufficient funds!\n");
            } else {
                printf("Invalid amount!\n");
            }
            break;
            
        case 4:
            printf("Thank you for using our ATM. Goodbye!\n");
            break;
            
        default:
            printf("Invalid option! Please select 1-4.\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int day;
    
    printf("Enter day number (1-7): ");
    scanf("%d", &day);
    
    switch (day) {
        case 1:
            printf("Monday\n");
            break;
        case 2:
            printf("Tuesday\n");
            break;
        case 3:
            printf("Wednesday\n");
            break;
        case 4:
            printf("Thursday\n");
            break;
        case 5:
            printf("Friday\n");
            break;
        case 6:
            printf("Saturday\n");
            break;
        case 7:
            printf("Sunday\n");
            break;
        default:
            printf("Invalid day! Please enter 1-7.\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int choice;
    float total = 0;
    
    printf("=== Restaurant Menu ===\n");
    printf("1. Burger - $8.99\n");
    printf("2. Pizza - $12.50\n");
    printf("3. Pasta - $9.75\n");
    printf("4. Salad - $6.25\n");
    printf("5. Drinks - $2.50\n");
    printf("6. Exit\n");
    printf("Enter your choice: ");
    scanf("%d", &choice);
    
    switch (choice) {
        case 1:
            total += 8.99;
            printf("Burger added to order!\n");
            printf("Total: $%.2f\n", total);
            break;
            
        case 2:
            total += 12.50;
            printf("Pizza added to order!\n");
            printf("Total: $%.2f\n", total);
            break;
            
        case 3:
            total += 9.75;
            printf("Pasta added to order!\n");
            printf("Total: $%.2f\n", total);
            break;
            
        case 4:
            total += 6.25;
            printf("Salad added to order!\n");
            printf("Total: $%.2f\n", total);
            break;
            
        case 5:
            total += 2.50;
            printf("Drinks added to order!\n");
            printf("Total: $%.2f\n", total);
            break;
            
        case 6:
            printf("Thank you for visiting!\n");
            break;
            
        default:
            printf("Invalid choice! Please select 1-6.\n");
    }
    return 0;
}

for (initialization; condition; increment/decrement) {
    // Code to repeat
}

#include <stdio.h>

int main() {
    int i;
    
    printf("Counting from 1 to 5:\n");
    
    for (i = 1; i <= 5; i++) {
        printf("%d ", i);
    }
    
    printf("\nLoop finished!\n");
    
    return 0;
}

#include <stdio.h>

int main() {
    int i;
    
    printf("Countdown: ");
    
    for (i = 10; i >= 1; i--) {
        printf("%d ", i);
    }
    
    printf("Blast off! 🚀\n");
    
    return 0;
}

#include <stdio.h>

int main() {
    int number, i;
    
    printf("Enter a number: ");
    scanf("%d", &number);
    
    printf("\nMultiplication table for %d:\n", number);
    printf("========================\n");
    
    for (i = 1; i <= 10; i++) {
        printf("%d x %d = %d\n", number, i, number * i);
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int i;
    
    // Count by 2s
    printf("Even numbers (2, 4, 6...): ");
    for (i = 2; i <= 20; i += 2) {
        printf("%d ", i);
    }
    
    printf("\n");
    
    // Count by 5s
    printf("Multiples of 5: ");
    for (i = 5; i <= 50; i += 5) {
        printf("%d ", i);
    }
    
    printf("\n");
    
    return 0;
}

#include <stdio.h>

int main() {
    int i, j;
    
    printf("Right triangle pattern:\n");
    
    for (i = 1; i <= 5; i++) {        // Outer loop for rows
        for (j = 1; j <= i; j++) {    // Inner loop for stars in each row
            printf("* ");
        }
        printf("\n");                  // New line after each row
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int i, j;
    int size;
    
    printf("Enter size of square: ");
    scanf("%d", &size);
    
    printf("\nNumber square pattern:\n");
    
    for (i = 1; i <= size; i++) {
        for (j = 1; j <= size; j++) {
            printf("%d ", j);
        }
        printf("\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int n, i;
    int sum = 0;
    
    printf("Enter a positive number: ");
    scanf("%d", &n);
    
    for (i = 1; i <= n; i++) {
        sum = sum + i;  // Add each number to sum
    }
    
    printf("Sum of numbers from 1 to %d = %d\n", n, sum);
    
    // Mathematical formula: sum = n * (n + 1) / 2
    printf("Verification using formula: %d\n", n * (n + 1) / 2);
    
    return 0;
}

#include <stdio.h>

int main() {
    int n, i;
    long long factorial = 1;  // Use long long for large numbers
    
    printf("Enter a number: ");
    scanf("%d", &n);
    
    if (n < 0) {
        printf("Factorial is not defined for negative numbers.\n");
    } else {
        for (i = 1; i <= n; i++) {
            factorial = factorial * i;
        }
        
        printf("Factorial of %d = %lld\n", n, factorial);
        
        // Show the calculation
        printf("Calculation: ");
        for (i = 1; i <= n; i++) {
            printf("%d", i);
            if (i < n) printf(" x ");
        }
        printf(" = %lld\n", factorial);
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int i, j;
    
    // Multiple variables
    for (i = 1, j = 10; i <= 5; i++, j--) {
        printf("i = %d, j = %d\n", i, j);
    }
    
    return 0;
}

int i = 1;              // Initialize outside
for ( ; i <= 5; ) {     // Empty initialization and increment
    printf("%d ", i);
    i++;                // Increment inside loop
}

#include <stdio.h>

int main() {
    int i;
    
    printf("Odd numbers between 1 and 20:\n");
    
    for (i = 1; i <= 20; i++) {
        if (i % 2 == 1) {  // Check if odd
            printf("%d ", i);
        }
    }
    
    printf("\n");
    
    // Alternative method
    printf("Alternative method:\n");
    for (i = 1; i <= 20; i += 2) {  // Start at 1, increment by 2
        printf("%d ", i);
    }
    
    printf("\n");
    
    return 0;
}

#include <stdio.h>

int main() {
    int i;
    int first = 0, second = 1, next;
    
    printf("First 10 terms of Fibonacci sequence:\n");
    
    // First two terms
    printf("%d %d ", first, second);
    
    // Calculate and print remaining 8 terms
    for (i = 3; i <= 10; i++) {
        next = first + second;
        printf("%d ", next);
        
        // Update for next iteration
        first = second;
        second = next;
    }
    
    printf("\n");
    
    return 0;
}

while (condition) {
    // Code to repeat
    // Don't forget to update the condition!
}

#include <stdio.h>

int main() {
    int i = 1;
    
    printf("Counting with while loop:\n");
    
    while (i <= 5) {
        printf("Count: %d\n", i);
        i++;  // IMPORTANT: increment i to avoid infinite loop
    }
    
    printf("Loop ended!\n");
    
    return 0;
}

#include <stdio.h>

int main() {
    int secret_number = 7;
    int guess;
    int attempts = 0;
    
    printf("=== Number Guessing Game ===\n");
    printf("I'm thinking of a number between 1 and 10.\n");
    
    while (guess != secret_number) {
        printf("Enter your guess: ");
        scanf("%d", &guess);
        attempts++;
        
        if (guess < secret_number) {
            printf("Too low! Try again.\n");
        } else if (guess > secret_number) {
            printf("Too high! Try again.\n");
        } else {
            printf("🎉 Congratulations! You guessed it!\n");
            printf("The number was %d.\n", secret_number);
            printf("You took %d attempts.\n", attempts);
        }
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int number;
    int sum = 0;
    int count = 0;
    
    printf("Enter numbers to add (enter 0 to stop):\n");
    
    while (1) {  // Infinite loop - we'll break out when needed
        printf("Enter number: ");
        scanf("%d", &number);
        
        if (number == 0) {
            break;  // Exit the loop
        }
        
        sum += number;
        count++;
        printf("Running total: %d\n", sum);
    }
    
    if (count > 0) {
        printf("\nFinal Results:\n");
        printf("Total sum: %d\n", sum);
        printf("Numbers entered: %d\n", count);
        printf("Average: %.2f\n", (float)sum / count);
    } else {
        printf("No numbers were entered.\n");
    }
    
    return 0;
}

do {
    // Code to repeat
    // This executes at least once
} while (condition);

#include <stdio.h>

int main() {
    int choice;
    
    do {
        printf("\n=== Student Management System ===\n");
        printf("1. Add Student\n");
        printf("2. View Students\n");
        printf("3. Delete Student\n");
        printf("4. Exit\n");
        printf("Enter your choice (1-4): ");
        scanf("%d", &choice);
        
        switch (choice) {
            case 1:
                printf("Adding new student...\n");
                break;
            case 2:
                printf("Displaying all students...\n");
                break;
            case 3:
                printf("Deleting student...\n");
                break;
            case 4:
                printf("Thank you for using our system!\n");
                break;
            default:
                printf("Invalid choice! Please try again.\n");
        }
        
    } while (choice != 4);  // Continue until user chooses to exit
    
    return 0;
}

#include <stdio.h>

int main() {
    int age;
    
    // Keep asking until valid age is entered
    do {
        printf("Enter your age (1-100): ");
        scanf("%d", &age);
        
        if (age < 1 || age > 100) {
            printf("Invalid age! Please enter between 1 and 100.\n");
        }
        
    } while (age < 1 || age > 100);
    
    printf("Thank you! Your age %d has been recorded.\n", age);
    
    // Determine category
    if (age < 13) {
        printf("Category: Child\n");
    } else if (age < 20) {
        printf("Category: Teenager\n");
    } else if (age < 60) {
        printf("Category: Adult\n");
    } else {
        printf("Category: Senior\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int i = 1;
    
    while (i <= 10) {
        if (i == 6) {
            printf("Breaking at %d\n", i);
            break;  // Exit loop when i is 6
        }
        printf("%d ", i);
        i++;
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int i = 0;
    
    while (i < 10) {
        i++;
        if (i % 2 == 0) {
            continue;  // Skip even numbers
        }
        printf("%d ", i);  // Only prints odd numbers
    }
    
    return 0;
}

// WRONG - infinite loop
int i = 1;
while (i <= 5) {
    printf("%d ", i);
    // Forgot to increment i!
}

// CORRECT
int i = 1;
while (i <= 5) {
    printf("%d ", i);
    i++;  // Don't forget this!
}

// Be careful with conditions
int i = 1;
while (i < 5) {    // This runs 4 times (1,2,3,4)
    printf("%d ", i);
    i++;
}

while (i <= 5) {   // This runs 5 times (1,2,3,4,5)
    printf("%d ", i);
    i++;
}

#include <stdio.h>

int main() {
    int number, i;
    
    printf("Enter a positive number: ");
    scanf("%d", &number);
    
    printf("Factors of %d are: ", number);
    
    i = 1;
    while (i <= number) {
        if (number % i == 0) {
            printf("%d ", i);
        }
        i++;
    }
    
    printf("\n");
    
    return 0;
}

#include <stdio.h>

int main() {
    int choice;
    float balance = 1000.00;
    float amount;
    
    do {
        printf("\n=== ATM Machine ===\n");
        printf("1. Check Balance\n");
        printf("2. Deposit Money\n");
        printf("3. Withdraw Money\n");
        printf("4. Exit\n");
        printf("Choose an option: ");
        scanf("%d", &choice);
        
        switch (choice) {
            case 1:
                printf("Your current balance: $%.2f\n", balance);
                break;
                
            case 2:
                printf("Enter deposit amount: $");
                scanf("%f", &amount);
                if (amount > 0) {
                    balance += amount;
                    printf("$%.2f deposited successfully!\n", amount);
                    printf("New balance: $%.2f\n", balance);
                } else {
                    printf("Invalid amount!\n");
                }
                break;
                
            case 3:
                printf("Enter withdrawal amount: $");
                scanf("%f", &amount);
                if (amount > 0 && amount <= balance) {
                    balance -= amount;
                    printf("$%.2f withdrawn successfully!\n", amount);
                    printf("Remaining balance: $%.2f\n", balance);
                } else if (amount > balance) {
                    printf("Insufficient funds!\n");
                } else {
                    printf("Invalid amount!\n");
                }
                break;
                
            case 4:
                printf("Thank you for using our ATM!\n");
                break;
                
            default:
                printf("Invalid choice! Please try again.\n");
        }
        
    } while (choice != 4);
    
    return 0;
}

return_type function_name(parameter_list) {
    // Function body
    return value;  // if return_type is not void
}

#include <stdio.h>

// Function declaration
void greet();

int main() {
    printf("Before calling function\n");
    greet();  // Function call
    printf("After calling function\n");
    
    return 0;
}

// Function definition
void greet() {
    printf("Hello! Welcome to C Programming!\n");
    printf("Have a great day!\n");
}

#include <stdio.h>

// Function declaration
void printInfo(char name[], int age);

int main() {
    // Function calls with different arguments
    printInfo("Alice", 25);
    printInfo("Bob", 30);
    printInfo("Carol", 22);
    
    return 0;
}

// Function definition
void printInfo(char name[], int age) {
    printf("Name: %s\n", name);
    printf("Age: %d years old\n", age);
    printf("Category: ");
    
    if (age < 18) {
        printf("Minor\n");
    } else if (age < 65) {
        printf("Adult\n");
    } else {
        printf("Senior\n");
    }
    
    printf("-------------------\n");
}

#include <stdio.h>

// Function declarations
int add(int a, int b);
float calculateArea(float length, float width);
int findMax(int x, int y, int z);

int main() {
    int sum;
    float area;
    int maximum;
    
    // Call functions and store return values
    sum = add(15, 25);
    area = calculateArea(5.5, 3.2);
    maximum = findMax(10, 25, 18);
    
    printf("Sum: %d\n", sum);
    printf("Area: %.2f\n", area);
    printf("Maximum: %d\n", maximum);
    
    return 0;
}

// Function to add two numbers
int add(int a, int b) {
    int result = a + b;
    return result;  // Return the sum
}

// Function to calculate rectangle area
float calculateArea(float length, float width) {
    return length * width;  // Direct return
}

// Function to find maximum of three numbers
int findMax(int x, int y, int z) {
    if (x >= y && x >= z) {
        return x;
    } else if (y >= x && y >= z) {
        return y;
    } else {
        return z;
    }
}

#include <stdio.h>

// Function declarations
float add(float a, float b);
float subtract(float a, float b);
float multiply(float a, float b);
float divide(float a, float b);
void displayMenu();

int main() {
    float num1, num2, result;
    int choice;
    
    do {
        displayMenu();
        printf("Enter your choice: ");
        scanf("%d", &choice);
        
        if (choice >= 1 && choice <= 4) {
            printf("Enter first number: ");
            scanf("%f", &num1);
            printf("Enter second number: ");
            scanf("%f", &num2);
        }
        
        switch (choice) {
            case 1:
                result = add(num1, num2);
                printf("%.2f + %.2f = %.2f\n", num1, num2, result);
                break;
            case 2:
                result = subtract(num1, num2);
                printf("%.2f - %.2f = %.2f\n", num1, num2, result);
                break;
            case 3:
                result = multiply(num1, num2);
                printf("%.2f * %.2f = %.2f\n", num1, num2, result);
                break;
            case 4:
                result = divide(num1, num2);
                if (num2 != 0) {
                    printf("%.2f / %.2f = %.2f\n", num1, num2, result);
                }
                break;
            case 5:
                printf("Thank you for using the calculator!\n");
                break;
            default:
                printf("Invalid choice! Please try again.\n");
        }
        printf("\n");
        
    } while (choice != 5);
    
    return 0;
}

void displayMenu() {
    printf("=== Calculator Menu ===\n");
    printf("1. Addition\n");
    printf("2. Subtraction\n");
    printf("3. Multiplication\n");
    printf("4. Division\n");
    printf("5. Exit\n");
}

float add(float a, float b) {
    return a + b;
}

float subtract(float a, float b) {
    return a - b;
}

float multiply(float a, float b) {
    return a * b;
}

float divide(float a, float b) {
    if (b != 0) {
        return a / b;
    } else {
        printf("Error: Division by zero!\n");
        return 0;
    }
}

#include <stdio.h>

// Function declarations
float calculateAverage(float marks[], int size);
char assignGrade(float average);
void displayResult(char name[], float average, char grade);
int countPassing(float marks[], int size);

int main() {
    char studentName[50];
    float marks[5];
    float average;
    char finalGrade;
    int passingCount;
    int i;
    
    printf("Enter student name: ");
    scanf("%s", studentName);
    
    printf("Enter marks for 5 subjects:\n");
    for (i = 0; i < 5; i++) {
        printf("Subject %d: ", i + 1);
        scanf("%f", &marks[i]);
    }
    
    // Call functions
    average = calculateAverage(marks, 5);
    finalGrade = assignGrade(average);
    passingCount = countPassing(marks, 5);
    
    // Display results
    displayResult(studentName, average, finalGrade);
    printf("Subjects passed: %d out of 5\n", passingCount);
    
    return 0;
}

float calculateAverage(float marks[], int size) {
    float sum = 0;
    int i;
    
    for (i = 0; i < size; i++) {
        sum += marks[i];
    }
    
    return sum / size;
}

char assignGrade(float average) {
    if (average >= 90) return 'A';
    else if (average >= 80) return 'B';
    else if (average >= 70) return 'C';
    else if (average >= 60) return 'D';
    else return 'F';
}

void displayResult(char name[], float average, char grade) {
    printf("\n=== Student Report ===\n");
    printf("Name: %s\n", name);
    printf("Average: %.2f%%\n", average);
    printf("Grade: %c\n", grade);
    
    if (grade != 'F') {
        printf("Status: PASS\n");
    } else {
        printf("Status: FAIL\n");
    }
}

int countPassing(float marks[], int size) {
    int count = 0;
    int i;
    
    for (i = 0; i < size; i++) {
        if (marks[i] >= 50) {  // Assuming 50 is passing marks
            count++;
        }
    }
    
    return count;
}

#include <stdio.h>

// Function declaration
int isPrime(int num);

int main() {
    int number;
    
    printf("Enter a number: ");
    scanf("%d", &number);
    
    if (isPrime(number)) {
        printf("%d is a prime number.\n", number);
    } else {
        printf("%d is not a prime number.\n", number);
    }
    
    return 0;
}

// Function to check if number is prime
int isPrime(int num) {
    int i;
    
    if (num <= 1) {
        return 0;  // Not prime
    }
    
    for (i = 2; i * i <= num; i++) {
        if (num % i == 0) {
            return 0;  // Not prime
        }
    }
    
    return 1;  // Prime
}

#include <stdio.h>

// Function declarations
float celsiusToFahrenheit(float celsius);
float fahrenheitToCelsius(float fahrenheit);
float celsiusToKelvin(float celsius);
float kelvinToCelsius(float kelvin);
void displayMenu();

int main() {
    int choice;
    float temperature, result;
    
    do {
        displayMenu();
        printf("Enter your choice: ");
        scanf("%d", &choice);
        
        if (choice >= 1 && choice <= 4) {
            printf("Enter temperature: ");
            scanf("%f", &temperature);
        }
        
        switch (choice) {
            case 1:
                result = celsiusToFahrenheit(temperature);
                printf("%.2f°C = %.2f°F\n", temperature, result);
                break;
            case 2:
                result = fahrenheitToCelsius(temperature);
                printf("%.2f°F = %.2f°C\n", temperature, result);
                break;
            case 3:
                result = celsiusToKelvin(temperature);
                printf("%.2f°C = %.2f K\n", temperature, result);
                break;
            case 4:
                result = kelvinToCelsius(temperature);
                printf("%.2f K = %.2f°C\n", temperature, result);
                break;
            case 5:
                printf("Goodbye!\n");
                break;
            default:
                printf("Invalid choice!\n");
        }
        
    } while (choice != 5);
    
    return 0;
}

void displayMenu() {
    printf("\n=== Temperature Converter ===\n");
    printf("1. Celsius to Fahrenheit\n");
    printf("2. Fahrenheit to Celsius\n");
    printf("3. Celsius to Kelvin\n");
    printf("4. Kelvin to Celsius\n");
    printf("5. Exit\n");
}

float celsiusToFahrenheit(float celsius) {
    return (celsius * 9.0 / 5.0) + 32;
}

float fahrenheitToCelsius(float fahrenheit) {
    return (fahrenheit - 32) * 5.0 / 9.0;
}

float celsiusToKelvin(float celsius) {
    return celsius + 273.15;
}

float kelvinToCelsius(float kelvin) {
    return kelvin - 273.15;
}

#include <stdio.h>

// Function declaration
long factorial(int n);

int main() {
    int number;
    
    printf("Enter a number: ");
    scanf("%d", &number);
    
    if (number < 0) {
        printf("Factorial is not defined for negative numbers.\n");
    } else {
        printf("Factorial of %d = %ld\n", number, factorial(number));
    }
    
    return 0;
}

// Recursive function to calculate factorial
long factorial(int n) {
    // Base case
    if (n == 0 || n == 1) {
        return 1;
    }
    
    // Recursive case
    return n * factorial(n - 1);
}

#include <stdio.h>

// Function declaration
int fibonacci(int n);

int main() {
    int n, i;
    
    printf("Enter number of terms: ");
    scanf("%d", &n);
    
    printf("Fibonacci sequence: ");
    for (i = 0; i < n; i++) {
        printf("%d ", fibonacci(i));
    }
    printf("\n");
    
    return 0;
}

// Recursive function for Fibonacci
int fibonacci(int n) {
    // Base cases
    if (n == 0) {
        return 0;
    }
    if (n == 1) {
        return 1;
    }
    
    // Recursive case
    return fibonacci(n - 1) + fibonacci(n - 2);
}

#include <stdio.h>

// Function declaration
int sumNatural(int n);

int main() {
    int number;
    
    printf("Enter a positive number: ");
    scanf("%d", &number);
    
    if (number < 1) {
        printf("Please enter a positive number.\n");
    } else {
        printf("Sum of first %d natural numbers = %d\n", 
               number, sumNatural(number));
    }
    
    return 0;
}

// Recursive function to find sum of natural numbers
int sumNatural(int n) {
    // Base case
    if (n == 1) {
        return 1;
    }
    
    // Recursive case
    return n + sumNatural(n - 1);
}

#include <stdio.h>

// Function declaration
double power(double base, int exponent);

int main() {
    double base;
    int exp;
    
    printf("Enter base: ");
    scanf("%lf", &base);
    printf("Enter exponent: ");
    scanf("%d", &exp);
    
    printf("%.2f raised to power %d = %.2f\n", 
           base, exp, power(base, exp));
    
    return 0;
}

// Recursive function to calculate power
double power(double base, int exponent) {
    // Base case
    if (exponent == 0) {
        return 1;
    }
    
    // Handle negative exponents
    if (exponent < 0) {
        return 1 / power(base, -exponent);
    }
    
    // Recursive case
    return base * power(base, exponent - 1);
}

if (exponent == 0) {
    return 1;
}

if (exponent < 0) {
    return 1 / power(base, -exponent);
}

 base * power(base, exponent - 1);

#include <stdio.h>

// Function declarations
int binarySearch(int arr[], int left, int right, int target);
void displayArray(int arr[], int size);

int main() {
    int arr[] = {2, 5, 8, 12, 16, 23, 38, 45, 56, 67, 78};
    int size = sizeof(arr) / sizeof(arr[0]);
    int target, result;
    
    printf("Array: ");
    displayArray(arr, size);
    
    printf("Enter number to search: ");
    scanf("%d", &target);
    
    result = binarySearch(arr, 0, size - 1, target);
    
    if (result != -1) {
        printf("Number %d found at index %d\n", target, result);
    } else {
        printf("Number %d not found in array\n", target);
    }
    
    return 0;
}

// Recursive binary search
int binarySearch(int arr[], int left, int right, int target) {
    // Base case: element not found
    if (left > right) {
        return -1;
    }
    
    int mid = left + (right - left) / 2;
    
    // Base case: element found
    if (arr[mid] == target) {
        return mid;
    }
    
    // Recursive cases
    if (target < arr[mid]) {
        return binarySearch(arr, left, mid - 1, target);  // Search left half
    } else {
        return binarySearch(arr, mid + 1, right, target);  // Search right half
    }
}

void displayArray(int arr[], int size) {
    int i;
    for (i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int binarySearch(int arr[], int left, int right, int target) {
    // Base case: element not found
    if (left > right) {
        return -1;
    }
    
    int mid = left + (right - left) / 2;
    
    // Base case: element found
    if (arr[mid] == target) {
        return mid;
    }
    
    // Recursive cases
    if (target < arr[mid]) {
        return binarySearch(arr, left, mid - 1, target);  // Search left half
    } else {
        return binarySearch(arr, mid + 1, right, target);  // Search right half
    }
}

long factorial(int n) {
    if (n <= 1) return 1;
    return n * factorial(n - 1);
}

long factorial(int n) {
    long result = 1;
    for (int i = 1; i <= n; i++) {
        result *= i;
    }
    return result;
}

// BAD - No base case
int badFunction(int n) {
    return badFunction(n - 1);  // Infinite recursion!
}

// GOOD - Has base case
int goodFunction(int n) {
    if (n <= 0) return 0;  // Base case
    return goodFunction(n - 1);
}

#include 

int memo[100] = {-1}; // Initialize with -1

int fibonacciMemo(int n) {
    if (n <= 1) return n;
    
    if (memo[n] != -1) {
        return memo[n];  // Return cached result
    }
    
    memo[n] = fibonacciMemo(n-1) + fibonacciMemo(n-2);
    return memo[n];
}

#include <stdio.h>

// Function declaration
int gcd(int a, int b);

int main() {
    int num1, num2;
    
    printf("Enter two numbers: ");
    scanf("%d %d", &num1, &num2);
    
    printf("GCD of %d and %d = %d\n", num1, num2, gcd(num1, num2));
    
    return 0;
}

// Recursive function to find GCD using Euclidean algorithm
int gcd(int a, int b) {
    // Base case
    if (b == 0) {
        return a;
    }
    
    // Recursive case
    return gcd(b, a % b);
}

int gcd(int a, int b) {
    // Base case
    if (b == 0) {
        return a;
    }
    
    // Recursive case
    return gcd(b, a % b);
}

#include <stdio.h>
#include <string.h>

// Function declarations
void reverseString(char str[], int start, int end);
void printString(char str[]);

int main() {
    char str[100];
    
    printf("Enter a string: ");
    gets(str);  // Read string with spaces
    
    printf("Original string: ");
    printString(str);
    
    reverseString(str, 0, strlen(str) - 1);
    
    printf("Reversed string: ");
    printString(str);
    
    return 0;
}

// Recursive function to reverse string
void reverseString(char str[], int start, int end) {
    // Base case
    if (start >= end) {
        return;
    }
    
    // Swap characters
    char temp = str[start];
    str[start] = str[end];
    str[end] = temp;
    
    // Recursive call
    reverseString(str, start + 1, end - 1);
}

void printString(char str[]) {
    printf("%s\n", str);
}

// Recursive function to reverse string
void reverseString(char str[], int start, int end) {
    // Base case
    if (start >= end) {
        return;
    }
    
    // Swap characters
    char temp = str[start];
    str[start] = str[end];
    str[end] = temp;
    
    // Recursive call
    reverseString(str, start + 1, end - 1);
}

#include <stdio.h>

int main() {
    // Array declaration and initialization
    int marks[5] = {85, 92, 78, 90, 88};
    int i;
    
    // Display array elements
    printf("Student marks:\n");
    for (i = 0; i < 5; i++) {
        printf("Student %d: %d\n", i + 1, marks[i]);
    }
    
    // Calculate and display sum and average
    int sum = 0;
    for (i = 0; i < 5; i++) {
        sum += marks[i];
    }
    
    float average = (float)sum / 5;
    
    printf("\nTotal marks: %d\n", sum);
    printf("Average marks: %.2f\n", average);
    
    return 0;
}

#include <stdio.h>

int main() {
    int size;
    int i;
    
    printf("Enter number of elements: ");
    scanf("%d", &size);
    
    int numbers[size];  // Variable-length array (C99 feature)
    
    // Input array elements
    printf("Enter %d numbers:\n", size);
    for (i = 0; i < size; i++) {
        printf("Element %d: ", i + 1);
        scanf("%d", &numbers[i]);
    }
    
    // Display array elements
    printf("\nYou entered:\n");
    for (i = 0; i < size; i++) {
        printf("numbers[%d] = %d\n", i, numbers[i]);
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int numbers[] = {45, 23, 67, 12, 89, 34, 78};
    int size = sizeof(numbers) / sizeof(numbers[0]);
    int i;
    
    // Initialize max and min with first element
    int max = numbers[0];
    int min = numbers[0];
    int maxIndex = 0;
    int minIndex = 0;
    
    // Find maximum and minimum
    for (i = 1; i < size; i++) {
        if (numbers[i] > max) {
            max = numbers[i];
            maxIndex = i;
        }
        if (numbers[i] < min) {
            min = numbers[i];
            minIndex = i;
        }
    }
    
    // Display array
    printf("Array: ");
    for (i = 0; i < size; i++) {
        printf("%d ", numbers[i]);
    }
    
    printf("\nMaximum value: %d (at index %d)\n", max, maxIndex);
    printf("Minimum value: %d (at index %d)\n", min, minIndex);
    
    return 0;
}

#include <stdio.h>

int main() {
    int numbers[] = {10, 25, 30, 45, 50, 65, 70};
    int size = sizeof(numbers) / sizeof(numbers[0]);
    int search, found = 0, position = -1;
    int i;
    
    // Display array
    printf("Array: ");
    for (i = 0; i < size; i++) {
        printf("%d ", numbers[i]);
    }
    
    printf("\nEnter number to search: ");
    scanf("%d", &search);
    
    // Linear search
    for (i = 0; i < size; i++) {
        if (numbers[i] == search) {
            found = 1;
            position = i;
            break;  // Exit loop once found
        }
    }
    
    // Display result
    if (found) {
        printf("Number %d found at index %d (position %d)\n", 
               search, position, position + 1);
    } else {
        printf("Number %d not found in the array\n", search);
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int numbers[] = {64, 34, 25, 12, 22, 11, 90};
    int size = sizeof(numbers) / sizeof(numbers[0]);
    int i, j, temp;
    
    printf("Original array: ");
    for (i = 0; i < size; i++) {
        printf("%d ", numbers[i]);
    }
    
    // Bubble sort algorithm
    for (i = 0; i < size - 1; i++) {
        for (j = 0; j < size - i - 1; j++) {
            if (numbers[j] > numbers[j + 1]) {
                // Swap elements
                temp = numbers[j];
                numbers[j] = numbers[j + 1];
                numbers[j + 1] = temp;
            }
        }
    }
    
    printf("\nSorted array: ");
    for (i = 0; i < size; i++) {
        printf("%d ", numbers[i]);
    }
    printf("\n");
    
    return 0;
}

for (i = 0; i < size - 1; i++) {           // Outer loop
    for (j = 0; j < size - i - 1; j++) {   // Inner loop
        if (numbers[j] > numbers[j + 1]) {
            // Swap elements
            temp = numbers[j];
            numbers[j] = numbers[j + 1];
            numbers[j + 1] = temp;
        }
    }
}

if (numbers[j] > numbers[j + 1]) {
    temp = numbers[j];              // Store first element
    numbers[j] = numbers[j + 1];    // Move second to first position  
    numbers[j + 1] = temp;          // Move first to second position
}

#include <stdio.h>

int main() {
    int source[] = {1, 2, 3, 4, 5};
    int destination[5];
    int size = 5;
    int i;
    
    // Copy array elements
    for (i = 0; i < size; i++) {
        destination[i] = source[i];
    }
    
    // Display both arrays
    printf("Source: ");
    for (i = 0; i < size; i++) {
        printf("%d ", source[i]);
    }
    
    printf("\nDestination: ");
    for (i = 0; i < size; i++) {
        printf("%d ", destination[i]);
    }
    printf("\n");
    
    return 0;
}

#include <stdio.h>

int main() {
    int numbers[] = {1, 2, 3, 4, 5, 6};
    int size = sizeof(numbers) / sizeof(numbers[^0]);
    int i, temp;
    
    printf("Original: ");
    for (i = 0; i < size; i++) {
        printf("%d ", numbers[i]);
    }
    
    // Reverse array
    for (i = 0; i < size / 2; i++) {
        temp = numbers[i];
        numbers[i] = numbers[size - 1 - i];
        numbers[size - 1 - i] = temp;
    }
    
    printf("\nReversed: ");
    for (i = 0; i < size; i++) {
        printf("%d ", numbers[i]);
    }
    printf("\n");
    
    return 0;
}

temp = numbers[0];           // temp = 1
numbers[0] = numbers[5];     // numbers[0] = 6  
numbers[5] = temp;           // numbers[5] = 1

temp = numbers[1];           // temp = 2
numbers[1] = numbers[4];     // numbers[1] = 5
numbers[4] = temp;           // numbers[4] = 2

temp = numbers[2];           // temp = 3
numbers[2] = numbers[3];     // numbers[2] = 4
numbers[3] = temp;           // numbers[3] = 3

#include <stdio.h>

// Function declarations
void displayArray(int arr[], int size);
int findSum(int arr[], int size);
float findAverage(int arr[], int size);
int findMax(int arr[], int size);

int main() {
    int marks[] = {85, 92, 78, 96, 88, 79, 91};
    int size = sizeof(marks) / sizeof(marks[0]);
    
    printf("Student Marks Analysis\n");
    printf("=====================\n");
    
    displayArray(marks, size);
    
    printf("Total marks: %d\n", findSum(marks, size));
    printf("Average: %.2f\n", findAverage(marks, size));
    printf("Highest mark: %d\n", findMax(marks, size));
    
    return 0;
}

void displayArray(int arr[], int size) {
    int i;
    printf("Marks: ");
    for (i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int findSum(int arr[], int size) {
    int sum = 0;
    int i;
    for (i = 0; i < size; i++) {
        sum += arr[i];
    }
    return sum;
}

float findAverage(int arr[], int size) {
    return (float)findSum(arr, size) / size;
}

int findMax(int arr[], int size) {
    int max = arr[0];
    int i;
    for (i = 1; i < size; i++) {
        if (arr[i] > max) {
            max = arr[i];
        }
    }
    return max;
}

#include <stdio.h>

int main() {
    int numbers[10];
    int i;
    int positive = 0, negative = 0, zero = 0;
    
    printf("Enter 10 integers:\n");
    for (i = 0; i < 10; i++) {
        printf("Number %d: ", i + 1);
        scanf("%d", &numbers[i]);
        
        if (numbers[i] > 0) {
            positive++;
        } else if (numbers[i] < 0) {
            negative++;
        } else {
            zero++;
        }
    }
    
    printf("\nArray: ");
    for (i = 0; i < 10; i++) {
        printf("%d ", numbers[i]);
    }
    
    printf("\n\nResults:\n");
    printf("Positive numbers: %d\n", positive);
    printf("Negative numbers: %d\n", negative);
    printf("Zero count: %d\n", zero);
    
    return 0;
}

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 2, 3, 4, 4, 5, 1, 6, 5};
    int size = sizeof(arr) / sizeof(arr[0]);
    int unique[size];
    int uniqueCount = 0;
    int i, j, isDuplicate;
    
    printf("Original array: ");
    for (i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    
    // Find unique elements
    for (i = 0; i < size; i++) {
        isDuplicate = 0;
        
        // Check if element already exists in unique array
        for (j = 0; j < uniqueCount; j++) {
            if (arr[i] == unique[j]) {
                isDuplicate = 1;
                break;
            }
        }
        
        // If not duplicate, add to unique array
        if (!isDuplicate) {
            unique[uniqueCount] = arr[i];
            uniqueCount++;
        }
    }
    
    printf("\nUnique elements: ");
    for (i = 0; i < uniqueCount; i++) {
        printf("%d ", unique[i]);
    }
    
    printf("\nTotal unique elements: %d\n", uniqueCount);
    
    return 0;
}

#include <stdio.h>

int main() {
    // Initialize a 3x4 matrix
    int matrix[3][4] = {
        {10, 20, 30, 40},
        {50, 60, 70, 80},
        {90, 100, 110, 120}
    };
    
    int rows = 3, cols = 4;
    int i, j;
    
    // Display the matrix
    printf("Matrix elements:\n");
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            printf("%4d ", matrix[i][j]);  // %4d for alignment
        }
        printf("\n");  // New line after each row
    }
    
    // Access specific elements
    printf("\nSpecific elements:\n");
    printf("matrix[0][0] = %d\n", matrix[0][0]);  // First element
    printf("matrix[1][2] = %d\n", matrix[1][2]);  // Second row, third column
    printf("matrix[2][3] = %d\n", matrix[2][3]);  // Last element
    
    return 0;
}

#include <stdio.h>

int main() {
    int matrix[3][12];
    int i, j;
    
    printf("Enter elements for a 3x3 matrix:\n");
    
    // Input matrix elements
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            printf("Enter element [%d][%d]: ", i, j);
            scanf("%d", &matrix[i][j]);
        }
    }
    
    // Display the matrix in proper format
    printf("\nMatrix you entered:\n");
    printf("-------------------\n");
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            printf("%4d ", matrix[i][j]);
        }
        printf("\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    // 4 students, 5 subjects each
    float grades[2][3];
    float studentTotal[2] = {0};
    float studentAverage[2];
    float subjectTotal[2] = {0};
    float subjectAverage[2];
    int students = 3, subjects = 2;
    int i, j;
    
    printf("Enter grades for 3 students (2 subjects each):\n");
    
    // Input grades
    for (i = 0; i < students; i++) {
        printf("\nStudent %d grades:\n", i + 1);
        for (j = 0; j < subjects; j++) {
            printf("Subject %d: ", j + 1);
            scanf("%f", &grades[i][j]);
        }
    }
    
    // Calculate totals and averages
    for (i = 0; i < students; i++) {
        for (j = 0; j < subjects; j++) {
            studentTotal[i] += grades[i][j];
            subjectTotal[j] += grades[i][j];
        }
        studentAverage[i] = studentTotal[i] / subjects;
    }
    
    for (j = 0; j < subjects; j++) {
        subjectAverage[j] = subjectTotal[j] / students;
    }
    
    // Display grade table
    printf("\n=== GRADE REPORT ===\n");
    printf("Student");
    for (j = 0; j < subjects; j++) {
        printf("  Sub%d", j + 1);
    }
    printf("  Total  Average\n");
    printf("-------------------------------\n");
    
    for (i = 0; i < students; i++) {
        printf("   %d   ", i + 1);
        for (j = 0; j < subjects; j++) {
            printf("%6.1f", grades[i][j]);
        }
        printf("%7.1f%8.2f\n", studentTotal[i], studentAverage[i]);
    }
    
    // Display subject averages
    printf("\nSubject Averages:\n");
    for (j = 0; j < subjects; j++) {
        printf("Subject %d: %.2f\n", j + 1, subjectAverage[j]);
    }
    
    return 0;
}

// Calculate totals and averages
for (i = 0; i < students; i++) {
    for (j = 0; j < subjects; j++) {
        studentTotal[i] += grades[i][j];
        subjectTotal[j] += grades[i][j];
    }
    studentAverage[i] = studentTotal[i] / subjects;
}
for (j = 0; j < subjects; j++) {
    subjectAverage[j] = subjectTotal[j] / students;
}

for (j = 0; j < subjects; j++) {
    subjectAverage[j] = subjectTotal[j] / students;
}

#include <stdio.h>

int main() {
    int matrixA[3][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
    int matrixB[3][3] = {{9, 8, 7}, {6, 5, 4}, {3, 2, 1}};
    int result[3][3];
    int i, j;
    
    // Matrix addition
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            result[i][j] = matrixA[i][j] + matrixB[i][j];
        }
    }
    
    // Display matrices
    printf("Matrix A:\n");
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            printf("%3d ", matrixA[i][j]);
        }
        printf("\n");
    }
    
    printf("\nMatrix B:\n");
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            printf("%3d ", matrixB[i][j]);
        }
        printf("\n");
    }
    
    printf("\nA + B =\n");
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 3; j++) {
            printf("%3d ", result[i][j]);
        }
        printf("\n");
    }
    
    return 0;
}

#include <stdio.h>

int main() {
    int matrix[3][4] = {
        {1, 2, 3, 4},
        {5, 6, 7, 8},
        {9, 10, 11, 12}
    };
    
    int transpose[4][3];  // Note: dimensions are swapped
    int i, j;
    
    // Calculate transpose
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 4; j++) {
            transpose[j][i] = matrix[i][j];
        }
    }
    
    // Display original matrix
    printf("Original Matrix (3x4):\n");
    for (i = 0; i < 3; i++) {
        for (j = 0; j < 4; j++) {
            printf("%3d ", matrix[i][j]);
        }
        printf("\n");
    }
    
    // Display transpose
    printf("\nTranspose Matrix (4x3):\n");
    for (i = 0; i < 4; i++) {
        for (j = 0; j < 3; j++) {
            printf("%3d ", transpose[i][j]);
        }
        printf("\n");
    }
    
    return 0;
}

#include <stdio.h>

// Function declarations (prototypes) - tell compiler about functions before main()
void displayBoard(char board[3][3]);    // Function to display the game board
int checkWinner(char board[3][3]);      // Function to check if there's a winner
int isBoardFull(char board[3][3]);      // Function to check if board is full (not implemented)

int main() {
    // Initialize 3x3 game board with empty spaces
    // Each cell contains a space character ' ' representing an empty square
    char board[3][3] = {
        {' ', ' ', ' '},    // Row 0: all empty
        {' ', ' ', ' '},    // Row 1: all empty
        {' ', ' ', ' '}     // Row 2: all empty
    };
    
    // Game variables
    int row, col;               // Store player's move coordinates (0-2 for each)
    char currentPlayer = 'X';   // Track current player (starts with X)
    int gameWon = 0;           // Flag: 0 = no winner, 1 = someone won
    int moves = 0;             // Counter for total moves made (max 9 for tie)
    
    // Display game title and instructions
    printf("=== TIC-TAC-TOE GAME ===\n");
    printf("Players: X and O\n");
    printf("Enter row (0-2) and column (0-2)\n\n");
    
    // Main game loop - continues until someone wins OR board is full (9 moves)
    while (!gameWon && moves < 9) {
        
        // Show current state of the board
        displayBoard(board);
        
        // Prompt current player for their move
        printf("Player %c's turn\n", currentPlayer);
        printf("Enter row and column: ");
        scanf("%d %d", &row, &col);    // Read two integers from user
        
        // INPUT VALIDATION
        // Check if coordinates are within valid range (0-2 for both row and col)
        if (row < 0 || row > 2 || col < 0 || col > 2) {
            printf("Invalid position! Try again.\n");
            continue;    // Skip rest of loop, start over
        }
        
        // Check if chosen position is already occupied
        if (board[row][col] != ' ') {
            printf("Position already taken! Try again.\n");
            continue;    // Skip rest of loop, start over
        }
        
        // MAKE THE MOVE
        board[row][col] = currentPlayer;    // Place X or O in chosen position
        moves++;                           // Increment total move counter
        
        // CHECK FOR WINNER
        gameWon = checkWinner(board);      // Call function to check winning conditions
        if (gameWon) {
            displayBoard(board);           // Show final board state
            printf("Player %c wins!\n", currentPlayer);
            break;                         // Exit game loop immediately
        }
        
        // SWITCH PLAYERS
        // Ternary operator: if current is 'X' then switch to 'O', else switch to 'X'
        currentPlayer = (currentPlayer == 'X') ? 'O' : 'X';
    }
    
    // Check for tie game (no winner and all 9 positions filled)
    if (!gameWon && moves == 9) {
        displayBoard(board);
        printf("It's a tie!\n");
    }
    
    return 0;    // End program successfully
}

// FUNCTION: Display the current game board with grid lines and coordinates
void displayBoard(char board[3][3]) {
    int i, j;    // Loop counters for rows and columns
    
    // Print column headers (0, 1, 2)
    printf("\n   0   1   2\n");
    
    // Loop through each row
    for (i = 0; i < 3; i++) {
        printf("%d ", i);    // Print row number
        
        // Loop through each column in current row
        for (j = 0; j < 3; j++) {
            printf(" %c ", board[i][j]);    // Print cell content (X, O, or space)
            if (j < 2) printf("|");         // Add vertical separator between columns
        }
        printf("\n");    // New line after each row
        
        // Add horizontal separator line between rows (but not after last row)
        if (i < 2) printf("  -----------\n");
    }
    printf("\n");    // Extra blank line for spacing
}

// FUNCTION: Check all possible winning combinations
int checkWinner(char board[3][3]) {
    int i;    // Loop counter
    
    // CHECK ROWS - look for three in a row horizontally
    for (i = 0; i < 3; i++) {
        // Check if all three cells in row i contain same non-empty character
        if (board[i][0] != ' ' &&           // First cell not empty AND
            board[i][0] == board[i][1] &&   // First equals second AND
            board[i][1] == board[i][2]) {   // Second equals third
            return 1;    // Winner found!
        }
    }
    
    // CHECK COLUMNS - look for three in a row vertically
    for (i = 0; i < 3; i++) {
        // Check if all three cells in column i contain same non-empty character
        if (board[0][i] != ' ' &&           // Top cell not empty AND
            board[0][i] == board[1][i] &&   // Top equals middle AND
            board[1][i] == board[2][i]) {   // Middle equals bottom
            return 1;    // Winner found!
        }
    }
    
    // CHECK DIAGONAL 1 - top-left to bottom-right
    if (board[0][0] != ' ' &&               // Top-left not empty AND
        board[0][0] == board[1][1] &&       // Top-left equals center AND
        board[1][1] == board[2][2]) {       // Center equals bottom-right
        return 1;    // Winner found!
    }
    
    // CHECK DIAGONAL 2 - top-right to bottom-left
    if (board[0][2] != ' ' &&               // Top-right not empty AND
        board[0][2] == board[1][1] &&       // Top-right equals center AND
        board[1][1] == board[2][0]) {       // Center equals bottom-left
        return 1;    // Winner found!
    }
    
    return 0;    // No winner found
}

// NOTE: isBoardFull() function was declared but never implemented
// It would check if all 9 positions are filled (alternative way to detect ties)

#include <stdio.h>

// FUNCTION: Display a matrix with proper formatting
// Parameters: matrix - 2D array with fixed 4 columns, rows - number of rows to display
// Note: In C, when passing 2D arrays to functions, all dimensions except the first must be specified
void displayMatrix(int matrix[][4], int rows) {  // Column size (4) must be specified
    int i, j;    // Loop counters for rows and columns
    
    // Outer loop: iterate through each row
    for (i = 0; i < rows; i++) {
        // Inner loop: iterate through each column in current row
        for (j = 0; j < 4; j++) {
            // Print each element with 4-character width for proper alignment
            // %4d ensures each number takes exactly 4 spaces (right-aligned)
            printf("%4d ", matrix[i][j]);
        }
        printf("\n");    // Move to next line after printing all columns in a row
    }
}

// FUNCTION: Calculate the sum of all elements in the matrix
// Parameters: matrix - 2D array with fixed 4 columns, rows - number of rows to process
// Returns: integer sum of all matrix elements
int matrixSum(int matrix[][4], int rows) {
    int sum = 0;     // Initialize sum accumulator to zero
    int i, j;        // Loop counters for rows and columns
    
    // Outer loop: iterate through each row
    for (i = 0; i < rows; i++) {
        // Inner loop: iterate through each column in current row
        for (j = 0; j < 4; j++) {
            // Add current element to running sum
            sum += matrix[i][j];    // Equivalent to: sum = sum + matrix[i][j]
        }
    }
    return sum;    // Return the total sum to calling function
}

int main() {
    // MATRIX INITIALIZATION
    // Declare and initialize a 3x4 matrix (3 rows, 4 columns)
    // Each row is initialized with specific values in curly braces
    int matrix[3][4] = {
        {1, 2, 3, 4},      // Row 0: elements 1, 2, 3, 4
        {5, 6, 7, 8},      // Row 1: elements 5, 6, 7, 8
        {9, 10, 11, 12}    // Row 2: elements 9, 10, 11, 12
    };
    
    // FUNCTION CALLS
    // Display the matrix in formatted output
    // Pass matrix name (which becomes a pointer) and number of rows (3)
    displayMatrix(matrix, 3);
    
    // Calculate and display the sum of all matrix elements
    // matrixSum() returns an integer which is directly used in printf()
    printf("Sum of all elements: %d\n", matrixSum(matrix, 3));
    
    return 0;    // Indicate successful program termination
}

#include <stdio.h>

int main() {
    // VARIABLE DECLARATIONS
    // Declare three 2x2 matrices: two input matrices and one result matrix
    int matrixA[2][2];      // First input matrix (2 rows, 2 columns)
    int matrixB[2][2];      // Second input matrix (2 rows, 2 columns)
    int result[2][2];       // Result matrix to store A × B
    
    // Loop counters: i for rows, j for columns, k for matrix multiplication inner loop
    int i, j, k;
    
    // INPUT SECTION: Get elements for first matrix
    printf("Enter elements for first 2x2 matrix:\n");
    
    // Nested loop to read elements for matrix A
    for (i = 0; i < 2; i++) {           // Loop through rows (0 to 1)
        for (j = 0; j < 2; j++) {       // Loop through columns (0 to 1)
            // Prompt user with specific position (row, column)
            printf("A[%d][%d]: ", i, j);
            // Read integer and store in matrix A at position [i][j]
            scanf("%d", &matrixA[i][j]);
        }
    }
    
    // INPUT SECTION: Get elements for second matrix
    printf("\nEnter elements for second 2x2 matrix:\n");
    
    // Nested loop to read elements for matrix B
    for (i = 0; i < 2; i++) {           // Loop through rows (0 to 1)
        for (j = 0; j < 2; j++) {       // Loop through columns (0 to 1)
            // Prompt user with specific position (row, column)
            printf("B[%d][%d]: ", i, j);
            // Read integer and store in matrix B at position [i][j]
            scanf("%d", &matrixB[i][j]);
        }
    }
    
    // MATRIX MULTIPLICATION ALGORITHM
    // Formula: C[i][j] = Σ(A[i][k] × B[k][j]) for k = 0 to n-1
    for (i = 0; i < 2; i++) {           // Loop through rows of result matrix
        for (j = 0; j < 2; j++) {       // Loop through columns of result matrix
            // Initialize current result cell to zero before accumulation
            result[i][j] = 0;
            
            // Inner loop for dot product calculation
            // Multiply corresponding elements and sum them up
            for (k = 0; k < 2; k++) {
                // Add product of A[i][k] and B[k][j] to running sum
                // This implements: result[i][j] = A[i][0]*B[0][j] + A[i][1]*B[1][j]
                result[i][j] += matrixA[i][k] * matrixB[k][j];
            }
        }
    }
    
    // OUTPUT SECTION: Display all matrices with proper formatting
    
    // Display Matrix A
    printf("\nMatrix A:\n");
    for (i = 0; i < 2; i++) {           // Loop through rows
        for (j = 0; j < 2; j++) {       // Loop through columns
            // Print each element with 4-character width for alignment
            printf("%4d ", matrixA[i][j]);
        }
        printf("\n");                   // New line after each row
    }
    
    // Display Matrix B
    printf("\nMatrix B:\n");
    for (i = 0; i < 2; i++) {           // Loop through rows
        for (j = 0; j < 2; j++) {       // Loop through columns
            // Print each element with 4-character width for alignment
            printf("%4d ", matrixB[i][j]);
        }
        printf("\n");                   // New line after each row
    }
    
    // Display Result Matrix (A × B)
    printf("\nA × B =\n");
    for (i = 0; i < 2; i++) {           // Loop through rows
        for (j = 0; j < 2; j++) {       // Loop through columns
            // Print each result element with 4-character width for alignment
            printf("%4d ", result[i][j]);
        }
        printf("\n");                   // New line after each row
    }
    
    return 0;    // Indicate successful program termination
}

#include <stdio.h>

int main() {
    // MATRIX DECLARATION AND INITIALIZATION
    // Declare and initialize a 3x4 matrix (3 rows, 4 columns) with predefined values
    int matrix[3][4] = {
        {45, 23, 78, 12},    // Row 0: contains values 45, 23, 78, 12
        {89, 34, 56, 67},    // Row 1: contains values 89, 34, 56, 67
        {15, 91, 38, 52}     // Row 2: contains values 15, 91, 38, 52
    };
    
    // VARIABLE DECLARATIONS
    int rows = 3, cols = 4;     // Matrix dimensions (3 rows, 4 columns)
    int i, j;                   // Loop counters for rows and columns
    
    // Variables to store maximum and minimum values
    int max, min;               // Store the actual maximum and minimum values
    
    // Variables to store positions of maximum and minimum elements
    int maxRow, maxCol;         // Row and column indices of maximum element
    int minRow, minCol;         // Row and column indices of minimum element
    
    // INITIALIZATION PHASE
    // Initialize max and min with first element of matrix
    // This gives us a starting point for comparison
    max = min = matrix[0][0];   // Both max and min start with matrix[0][0] value
    
    // Initialize position variables to point to first element [0][0]
    maxRow = maxCol = minRow = minCol = 0;
    
    // SEARCH ALGORITHM: Find maximum and minimum elements
    // Use nested loops to traverse entire matrix
    for (i = 0; i < rows; i++) {        // Outer loop: iterate through each row
        for (j = 0; j < cols; j++) {    // Inner loop: iterate through each column
            
            // CHECK FOR NEW MAXIMUM
            // If current element is greater than current max, update max and its position
            if (matrix[i][j] > max) {
                max = matrix[i][j];     // Update maximum value
                maxRow = i;             // Update row position of maximum
                maxCol = j;             // Update column position of maximum
            }
            
            // CHECK FOR NEW MINIMUM  
            // If current element is smaller than current min, update min and its position
            if (matrix[i][j] < min) {
                min = matrix[i][j];     // Update minimum value
                minRow = i;             // Update row position of minimum
                minCol = j;             // Update column position of minimum
            }
        }
    }
    
    // OUTPUT SECTION: Display results
    
    // Display the entire matrix in formatted layout
    printf("Matrix:\n");
    for (i = 0; i < rows; i++) {        // Loop through each row
        for (j = 0; j < cols; j++) {    // Loop through each column in current row
            // Print each element with 4-character width for proper alignment
            printf("%4d ", matrix[i][j]);
        }
        printf("\n");                   // Move to next line after completing a row
    }
    
    // Display maximum element and its position
    // Format: value at position [row][column]
    printf("\nLargest element: %d at position [%d][%d]\n", 
           max, maxRow, maxCol);
    
    // Display minimum element and its position  
    // Format: value at position [row][column]
    printf("Smallest element: %d at position [%d][%d]\n", 
           min, minRow, minCol);
    
    return 0;    // Indicate successful program termination
}

char name[6] = {'H', 'e', 'l', 'l', 'o', '\0'};

char name[] = "Hello"; // Size automatically calculated
char name[10] = "Hello"; // Size specified (allows for longer strings later)

#include <stdio.h>
#include <string.h>

int main() {
    // Different ways to declare strings
    char greeting[] = "Hello World!";
    char name[50] = "Alice";
    char message[100];
    
    printf("Greeting: %s\n", greeting);
    printf("Name: %s\n", name);
    
    // Get string length
    printf("Length of greeting: %lu\n", strlen(greeting));
    printf("Length of name: %lu\n", strlen(name));
    
    // Copy strings
    strcpy(message, "Welcome to C Programming!");
    printf("Message: %s\n", message);
    
    // String concatenation
    strcat(name, " Johnson");
    printf("Full name: %s\n", name);
    
    return 0;
}

#include <stdio.h>

int main() {
    char name[50];
    char city[50];
    char address[100];

    // Method 1: scanf() - stops at space
    printf("Enter your first name: ");
    scanf("%s", name); // No & needed for strings

    // Clear input buffer
    while (getchar() != '\n');

    // Method 2: gets() - reads entire line (including spaces)
    printf("Enter your city: ");
    gets(city);

    // Method 3: fgets() - safer than gets()
    printf("Enter your address: ");
    fgets(address, sizeof(address), stdin);

    printf("\n=== Your Information ===\n");
    printf("Name: %s\n", name);
    printf("City: %s\n", city);
    printf("Address: %s", address); // fgets includes \n

    return 0;
}

#include <stdio.h>
#include <string.h>

int main() {
    // STRING VARIABLE DECLARATIONS
    char str1[50] = "Hello";   // String initialized with "Hello"
    char str2[50] = "World";   // String initialized with "World"
    char str3[50];             // Empty string for copy operations
    char str4[50] = "hello";   // String with lowercase "hello" (to show comparison)

    printf("=== STRING FUNCTIONS DEMO ===\n");

    // 1. strlen() - Find the length of a string
    // %lu format specifier for unsigned long returned by strlen()
    printf("strlen(\"%s\") = %lu\n", str1, strlen(str1));
    // Output: strlen("Hello") = 5

    // 2. strcpy() - Copy str1 into str3
    strcpy(str3, str1);  // str3 now contains "Hello"
    printf("After strcpy(str3, str1): str3 = \"%s\"\n", str3);

    // 3. strcat() - Concatenate (append) str2 to str1
    strcat(str1, str2);  // str1 becomes "HelloWorld"
    printf("After strcat(str1, str2): str1 = \"%s\"\n", str1);

    // Reset str1 for further operations (otherwise it remains "HelloWorld")
    strcpy(str1, "Hello");

    // 4. strcmp() - Compare two strings (case-sensitive)
    // Returns: 0 if equal, <0 if first < second, >0 if first > second (ASCII order)
    printf("strcmp(\"%s\", \"%s\") = %d\n", str1, str2, strcmp(str1, str2));  // "Hello" vs "World"
    printf("strcmp(\"%s\", \"%s\") = %d\n", str1, str1, strcmp(str1, str1));  // "Hello" vs "Hello"
    printf("strcmp(\"%s\", \"%s\") = %d\n", str1, str4, strcmp(str1, str4));  // "Hello" vs "hello" (case sensitive)

    // 5. strchr() - Find first occurrence of character in a string
    // Returns pointer to the character if found, else NULL
    char *pos = strchr(str1, 'e');  // Looks for 'e' in "Hello"
    if (pos != NULL) {
        // To get character position as index: subtract start address of str1
        printf("Character 'e' found at position: %ld\n", pos - str1);
    }

    // 6. strstr() - Find substring within another string
    // Returns pointer to first occurrence, else NULL
    char sentence[] = "C programming is fun";
    char *found = strstr(sentence, "program");
    if (found != NULL) {
        printf("\"program\" found in: \"%s\"\n", sentence);
    }

    return 0;  // Indicate successful execution
}

#include <stdio.h>
#include <string.h>
#include <ctype.h>  // For character functions

int main() {
    char text[200];
    int length, i;
    int vowels = 0, consonants = 0, digits = 0, spaces = 0, others = 0;
    
    printf("Enter a sentence: ");
    fgets(text, sizeof(text), stdin);
    
    // Remove newline from fgets
    text[strcspn(text, "\n")] = 0;
    
    length = strlen(text);
    
    // Analyze each character
    for (i = 0; i < length; i++) {
        char ch = tolower(text[i]);  // Convert to lowercase
        
        if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') {
            vowels++;
        } else if (ch >= 'a' && ch <= 'z') {
            consonants++;
        } else if (ch >= '0' && ch <= '9') {
            digits++;
        } else if (ch == ' ') {
            spaces++;
        } else {
            others++;
        }
    }
    
    // Display results
    printf("\n=== TEXT ANALYSIS ===\n");
    printf("Original text: \"%s\"\n", text);
    printf("Total characters: %d\n", length);
    printf("Vowels: %d\n", vowels);
    printf("Consonants: %d\n", consonants);
    printf("Digits: %d\n", digits);
    printf("Spaces: %d\n", spaces);
    printf("Other characters: %d\n", others);
    
    return 0;
}

#include <stdio.h>
#include <string.h>
#include <ctype.h>  // For character functions

// REVERSE the string in place (e.g., "Hello" -> "olleH")
void reverseString(char str[]) {
    int len = strlen(str);      // Get length of the string (not counting '\0')
    int i;
    // Swap characters from ends moving toward center (only up to the halfway point)
    for (i = 0; i < len / 2; i++) {
        char temp = str[i];                 // Temporary hold left character
        str[i] = str[len - 1 - i];          // Move right character to left
        str[len - 1 - i] = temp;            // Move left character to right
    }
}

// Convert all string characters to UPPERCASE (in place)
void toUpperCase(char str[]) {
    int i;
    // Step through each character until end of string ('\0')
    for (i = 0; str[i] != '\0'; i++)
        str[i] = toupper(str[i]);           // Convert to uppercase using ctype.h
}

// Convert all string characters to LOWERCASE (in place)
void toLowerCase(char str[]) {
    int i;
    // Step through each character
    for (i = 0; str[i] != '\0'; i++)
        str[i] = tolower(str[i]);           // Convert to lowercase
}

// Count the number of WORDS in a string (words separated by whitespace)
int countWords(char str[]) {
    int count = 0, inWord = 0, i;
    // Loop through each character of the string
    for (i = 0; str[i] != '\0'; i++) {
        // If character is NOT a space, tab, or newline, we're inside a word
        if (str[i] != ' ' && str[i] != '\t' && str[i] != '\n') {
            if (!inWord) {      // If we weren't in a word before, new word starts here
                count++;        // Increment word count
                inWord = 1;     // Now we are inside a word
            }
        } else {
            inWord = 0;         // We hit space/tab/newline, so we're outside a word
        }
    }
    return count;
}

int main() {
    char original[] = "Hello";          // Original string to manipulate
    char copy1[50], copy2[50], copy3[50];  // Copies (large size for safety)

    strcpy(copy1, original);    // Make a copy for reversal
    strcpy(copy2, original);    // Make a copy for uppercase conversion
    strcpy(copy3, original);    // Make a copy for lowercase conversion

    printf("Original string: \"%s\"\n", original);
    printf("Word count: %d\n", countWords(original));    // Count how many words

    // Reverse and print
    reverseString(copy1);
    printf("Reversed: \"%s\"\n", copy1);

    // Convert to uppercase and print
    toUpperCase(copy2);
    printf("Uppercase: \"%s\"\n", copy2);

    // Convert to lowercase and print
    toLowerCase(copy3);
    printf("Lowercase: \"%s\"\n", copy3);

    return 0;           // End program
}

#include <stdio.h>
#include <string.h>

int main() {
    // Declare a 2D char array to store up to 5 student names, each up to 29 characters (+1 for '\0')
    char students[5][30];
    int numStudents = 0;      // Tracks the number of students currently in the list
    int choice;               // For user menu selection
    int i;                    // General-purpose loop index
    char searchName[30];      // Buffer to store name being searched
    int found;                // Flag to indicate if search result is found

    do {
        // Display menu
        printf("\n=== STUDENT NAME MANAGER ===\n");
        printf("1. Add Student\n");
        printf("2. Display All Students\n");
        printf("3. Search Student\n");
        printf("4. Exit\n");
        printf("Choice: ");
        scanf("%d", &choice);

        switch (choice) {
            // Add new student name
            case 1:
                if (numStudents < 5) { // Prevent array overflow
                    printf("Enter student name: ");
                    // Reads a word (no spaces) into next empty slot
                    scanf("%s", students[numStudents]);
                    numStudents++;    // Increment student count
                    printf("Student added successfully!\n");
                } else {
                    printf("Maximum students reached!\n");
                }
                break;

            // Display all saved student names
            case 2:
                if (numStudents == 0) {
                    printf("No students found!\n");
                } else {
                    printf("\nList of Students:\n");
                    // Loop through each name and print it
                    for (i = 0; i < numStudents; i++) {
                        printf("%d. %s\n", i + 1, students[i]);
                    }
                }
                break;

            // Search for a student by name
            case 3:
                printf("Enter name to search: ");
                scanf("%s", searchName);
                found = 0; // Assume not found
                // Loop and compare each saved name to target
                for (i = 0; i < numStudents; i++) {
                    // strcmp returns 0 if strings match exactly
                    if (strcmp(students[i], searchName) == 0) {
                        printf("Student '%s' found at position %d\n", 
                               searchName, i + 1);
                        found = 1; // Mark as found
                        break;     // No need to continue searching
                    }
                }
                if (!found) {
                    printf("Student '%s' not found!\n", searchName);
                }
                break;

            // Exit the loop/program
            case 4:
                printf("Goodbye!\n");
                break;

            // Handle invalid choices
            default:
                printf("Invalid choice!\n");
        }
    } while (choice != 4); // Repeat until the user chooses to exit

    return 0; // End the program successfully
}

#include <stdio.h>
#include <string.h>
#include <ctype.h>

// Function to check if a string is a palindrome (case-insensitive)
int isPalindrome(char str[]) {
    int len = strlen(str);     // Get length of the string
    int i;                    // Loop counter

    // Compare characters from start and end moving inwards
    for (i = 0; i < len / 2; i++) {
        // Convert both characters to lowercase and compare
        // If any pair doesn't match, it's not a palindrome
        if (tolower(str[i]) != tolower(str[len - 1 - i])) {
            return 0;         // Not a palindrome
        }
    }
    return 1;                 // All pairs matched: it's a palindrome
}

int main() {
    char word[100];           // Buffer to store user input (up to 99 characters + null terminator)

    printf("Enter a word: ");
    scanf("%s", word);        // Read a single word (no spaces) from user

    // Call isPalindrome to check, and display message accordingly
    if (isPalindrome(word)) {
        printf("'%s' is a palindrome!\n", word);
    } else {
        printf("'%s' is not a palindrome.\n", word);
    }

    return 0;                 // Return 0 to indicate success
}

#include <stdio.h>
#include <string.h>

int main() {
    // Declare a character array to store the user input text (maximum 99 characters + 1 for '\0')
    char text[100];

    // Declare and initialize an array to store frequency of each character (ASCII 0 to 255)
    // All elements start at 0
    int frequency[256] = {0};

    int i; // Loop counter

    // Prompt the user to enter a string
    printf("Enter text: ");

    // Read a line of text (up to 99 characters) from standard input
    // fgets includes whitespace and stops at newline or buffer full
    fgets(text, sizeof(text), stdin);

    // Loop through each character of the input string
    for (i = 0; text[i] != '\0'; i++) {
        // Increment the frequency for the ASCII value of current character
        frequency[(int)text[i]]++;
    }

    // Display the character frequencies (ignoring the newline character)
    printf("\nCharacter frequencies:\n");

    // Loop through all ASCII values
    for (i = 0; i < 256; i++) {
        // Only print characters that occurred at least once AND are not the newline
        if (frequency[i] > 0 && i != '\n') { // '\n' has ASCII value 10
            printf("'%c': %d\n", i, frequency[i]);
        }
    }

    return 0; // Program ended successfully
}

#include <stdio.h>
#include <ctype.h>
#include <string.h>

int main() {
    char sentence[200];
    int i;
    int newWord = 1;  // Flag to indicate start of new word
    
    printf("Enter a sentence: ");
    fgets(sentence, sizeof(sentence), stdin);
    
    for (i = 0; sentence[i] != '\0'; i++) {
        if (sentence[i] == ' ' || sentence[i] == '\t' || sentence[i] == '\n') {
            newWord = 1;  // Next non-space character starts a new word
        } else if (newWord) {
            sentence[i] = toupper(sentence[i]);  // First letter uppercase
            newWord = 0;
        } else {
            sentence[i] = tolower(sentence[i]);  // Rest lowercase
        }
    }
    
    printf("Title case: %s", sentence);
    
    return 0;
}

#include <stdio.h>
#include <string.h>

int main() {
    char original[100];
    char noSpaces[100];
    int i, j = 0;
    
    printf("Enter a string: ");
    fgets(original, sizeof(original), stdin);
    
    // Remove newline from fgets
    original[strcspn(original, "\n")] = 0;
    
    // Copy non-space characters
    for (i = 0; original[i] != '\0'; i++) {
        if (original[i] != ' ') {
            noSpaces[j] = original[i];
            j++;
        }
    }
    noSpaces[j] = '\0';  // Null terminate
    
    printf("Original: \"%s\"\n", original);
    printf("No spaces: \"%s\"\n", noSpaces);
    printf("Removed %lu spaces\n", strlen(original) - strlen(noSpaces));
    
    return 0;
}

int a = 5;
int *ptr; // Declaration
ptr = &a; // Store address of a in ptr

#include <stdio.h>

    int main() {
    int num = 10;
    int *p;
    p = #
    printf("Value of num: %d\\n", num);
    printf("Address of num: %p\\n", &num);
    printf("Pointer p stores address: %p\\n", p);
    printf("Value at address p: %d\\n", *p);
    return 0;
    }

#include <stdio.h>

int main() {
    int x = 25;
    int *px = &x;
    *px = 50; // Changes value of x through pointer

    printf("x = %d\\n", x);       // 50
    printf("*px = %d\\n", *px);   // 50
    return 0;
}

#include <stdio.h>

    int main() {
    int arr[3] = {10, 20, 30};
    int *ptr = arr;

    printf("%d\\n", *ptr); // 10
    ptr++; // Moves to next int in array
    printf("%d\\n", *ptr); // 20
    return 0;
    }

#include <stdio.h>

int main() {
    int n = 100;
    int *p = &n;
    printf("Value: %d\n", *p);
    return 0;
    }

#include <stdio.h>

int main() {
    float f = 12.34;
    float *pf = &f;
    *pf = 99.99;
    printf("%.2f\n", f);
    return 0;
}

struct Student {
    char name[50];
    int age;
    float marks;
};

#include <stdio.h>

// Define a structure called "Student" 
// This creates a new user-defined data type
struct Student {
    char name[20];  
    int age;          
    float marks;      
};

int main() {
    // Create and initialize a structure variable 's1' of type 'Student'
    // This uses aggregate initialization with curly braces
    struct Student s1 = {"John", 18, 92.5};
    
    // Access and print the name member using dot notation
    printf("Name: %s\n", s1.name);
    
    // Access and print the age member using dot notation
     printf("Age: %d\n", s1.age);
    
    // Access and print the marks member using dot notation
    printf("Marks: %.2f\n", s1.marks);
    
    return 0;    // Indicates successful program execution
}

#include <stdio.h>

struct Point {
    int x;
    int y;
};
int main() {
    struct Point points[2] = {{1,2}, {3,4}};
    for(int i = 0; i < 2; i++) {
        printf("(%d, %d)\\n", points[i].x, points[i].y);
    }
    return 0;
}

struct Point points[9] = {{1,2}, {3,4}};

printf("(%d, %d)\n", points[i].x, points[i].y);

#include <stdio.h>
    
struct Date {
    int day, month, year;
};
struct Student {
    char name[10];
    struct Date dob;
};

int main() {
    struct Student s = {"Jane", {15, 8, 2005}};
    printf("%s: %d/%d/%d\\n", s.name, s.dob.day, s.dob.month, s.dob.year);
    return 0;
}

union Number {
    int i;
    float f;
};

#include <stdio.h>
union Data {
    int i;
    float f;
    char c;
};
int main() {
    union Data d;
    d.i = 25;
    printf("%d\\n", d.i);
    d.f = 45.5;
    printf("%.2f\\n", d.f);
    d.c = 'A';
    printf("%c\\n", d.c);
    return 0;
}

#include <stdio.h>

struct Book {
    char title[50];
    char author[50];
    float price;
};
int main() {
    struct Book b = {"C Guide", "S. Kumar", 299.50};
    printf("%s by %s costs %.2f\n", b.title, b.author, b.price);
    return 0;
}

                                    

#include <stdio.h>

union Number {
    int i;
    float f;
};
int main() {
    union Number n;
    n.i = 10;
    printf("i: %d\n", n.i);
    n.f = 5.5;
    // Now, n.i will be overwritten
    printf("f: %.2f\n", n.f);
    printf("i (after assigning f): %d", n.i);
    return 0;
}

#include <stdio.h>

int main() {
    FILE *fp = fopen("output.txt", "w");   // Open (or create) output.txt in write mode; returns a FILE* or NULL on failure
    if (fp == NULL) {                      // Check if the file failed to open
        printf("File not created!\n");     // Inform about the error
        return 1;                          // Exit with non-zero status indicating failure
    }

    // Write formatted text to the file (like printf but targets the file stream fp)
    fprintf(fp, "Hello, File!\nThis is a file writing example.");

    fclose(fp);                             // Always close the file to flush buffers and free resources

    printf("Done writing.\n");              // Inform the user that writing is complete
    return 0;                               
}

#include <stdio.h>

int main() {
    char buffer[100];
    FILE *fp = fopen("output.txt", "r");
    if (fp == NULL) {
        printf("File couldn't be opened!\\n");
        return 1;
    }
    while (fgets(buffer, sizeof(buffer), fp) != NULL) {
        printf("%s", buffer);
    }
    fclose(fp);
    return 0;
}

#include <stdio.h>

int main() {
    char buffer[100];
    FILE *fp = fopen("output.txt", "r");
    if (fp == NULL) {
        printf("File couldn't be opened!\\n");
        return 1;
    }
    while (fgets(buffer, sizeof(buffer), fp) != NULL) {
        printf("%s", buffer);
    }
    fclose(fp);
    return 0;
}

#include <stdio.h>

int main() {
    FILE *fp = fopen("info.txt", "w");
    fprintf(fp, "Name: Alex\nAge: 23\n");
    fclose(fp);
    return 0;
}
                    

#include <stdio.h>

int main() {
    char line[50];
    FILE *fp = fopen("info.txt", "r");
    while (fgets(line, sizeof(line), fp) != NULL) {
        printf("%s", line);
    }
    fclose(fp);
    return 0;
}