Do-While Loop

The do-while loop is a special type of loop in C that guarantees the loop body executes at least once, regardless of the condition. Think of it like this: "Do something first, then check if you should continue doing it."

Syntax

do {
    // Code to be executed
} while (condition);

Notice the semicolon (;) after the while statement - it's required!

How It Works

1. Execute the code block first
2. Check the condition after execution
3. If the condition is true, repeat from step 1
4. If the condition is false, exit the loop

Key Difference from While Loop

While Loop	Do-While Loop
Checks condition before execution	Checks condition after execution
May execute 0 or more times	Always executes at least once

Basic Example

#include <stdio.h>

int main() {
    int count = 1;
    
    do {
        printf("Count: %d\n", count);
        count++;
    } while (count <= 3);
    
    return 0;
}

Output:

Count: 1
Count: 2
Count: 3

Real-World Example: Menu System

Do-while loops are perfect for menu systems where you want to show the menu at least once:

#include <stdio.h>

int main() {
    int choice;
    
    do {
        printf("\n=== MENU ===\n");
        printf("1. Play Game\n");
        printf("2. View Scores\n");
        printf("3. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);
        
        switch(choice) {
            case 1:
                printf("Starting game...\n");
                break;
            case 2:
                printf("Displaying scores...\n");
                break;
            case 3:
                printf("Goodbye!\n");
                break;
            default:
                printf("Invalid choice! Try again.\n");
        }
    } while (choice != 3);
    
    return 0;
}

Example: Input Validation

#include <stdio.h>

int main() {
    int number;
    
    do {
        printf("Enter a positive number: ");
        scanf("%d", &number);
        
        if (number <= 0) {
            printf("That's not positive! Try again.\n");
        }
    } while (number <= 0);
    
    printf("Great! You entered: %d\n", number);
    return 0;
}

When to Use Do-While Loop

✅ Use do-while when:

• You need the code to run at least once
• Creating menu systems
• Input validation scenarios
• Game loops that should run once before checking conditions

❌ Don't use do-while when:

• The loop might not need to execute at all
• You want to check the condition before the first execution

Common Pitfall

Remember the semicolon after while(condition)! This is a common mistake:

// ❌ Wrong - missing semicolon
do {
    printf("Hello\n");
} while (condition)  // Missing semicolon!

// ✅ Correct
do {
    printf("Hello\n");
} while (condition);  // Semicolon is required

The do-while loop is your go-to choice when you're certain that your code block needs to execute at least once before any condition checking takes place!