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🔁 C++ do-while Loop – Execute Then Check Condition

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🧲 Introduction – What Is a do-while Loop in C++?

The do-while loop in C++ is a control structure that executes the loop body at least once, and then checks the condition to decide whether to repeat. It is ideal when the loop must run at least one time regardless of the condition.

🎯 In this guide, you’ll learn:

• Syntax and execution flow of do-while
• Use cases where it’s better than while
• Examples and nested patterns
• Common mistakes and loop control tips

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✅ Syntax of do-while Loop

do {
    // code block
} while (condition);

📌 Note the semicolon (;) after the while.

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✏️ Example – Basic do-while Loop

int i = 1;

do {
    cout << i << " ";
    i++;
} while (i <= 5);

Output:

1 2 3 4 5

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🔁 Flow of Execution

1. Execute the loop block
2. Evaluate the condition
3. If condition is true, repeat from step 1
4. If condition is false, exit loop

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🔁 Input Validation Example

int num;

do {
    cout << "Enter a number (0 to exit): ";
    cin >> num;
    cout << "You entered: " << num << endl;
} while (num != 0);

✅ Ensures the user is prompted at least once.

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🔁 Nested do-while Loops

int row = 1;

do {
    int col = 1;
    do {
        cout << "* ";
        col++;
    } while (col <= 3);

    cout << endl;
    row++;
} while (row <= 2);

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⚠️ Common Mistakes

❌ Mistake	✅ Fix
Missing semicolon after while()	Add ; after the condition
Skipping update inside loop	Ensure condition variable is updated
Infinite loop	Ensure the loop eventually meets the stop condition

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🧠 Best Practices

• Use do-while when at least one execution is required
• Make sure the condition can eventually fail
• Add a break option for user-controlled exits

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📌 Summary – Recap & Next Steps

🔍 Key Takeaways:

• do-while loops execute at least once
• Condition is checked after the first run
• Ideal for menu prompts, form re-entry, and retry logic
• Remember the semicolon after while

⚙️ Real-World Relevance:
Used in input loops, retry systems, and interactive menus that must appear before conditions are evaluated.

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❓ FAQs – C++ do-while Loop

❓ How is do-while different from while?
✅ do-while runs at least once. while might never run.

❓ Can I use break in do-while loops?
✅ Yes. break exits the loop immediately.

❓ Is the condition required in do-while?
✅ Yes. The condition determines if the loop repeats.

❓ Can I use continue in a do-while loop?
✅ Yes. It jumps to the condition check for the next iteration.

❓ Should I always use do-while for input validation?
✅ It’s a great choice when you want at least one prompt shown to the user.

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