PHP Do…While Loop – Syntax, Examples & Best Practices

A practical guide to using the do...while loop in PHP for guaranteed one-time execution.

Introduction – Why Use the do...while Loop?

The do...while loop in PHP is useful when you want your code block to run at least once, even if the condition is false. It’s perfect for input validation, authentication attempts, or any process that should execute before checking the condition.

In this guide, you’ll learn:

• The structure and syntax of do...while
• Key differences between while and do...while
• Practical examples and real-world use cases
• Loop control with break and continue
• Best practices for reliability and readability

Basic Syntax of do...while

$i = 1;

do {
    echo "Step: $i <br>";
    $i++;
} while ($i <= 3);

Output:

Step: 1
Step: 2
Step: 3

Explanation: Code inside do runs first, then condition is checked.

When the Condition is Initially False

$i = 5;

do {
    echo "Run once even if condition fails.";
} while ($i < 3);

Output:

Run once even if condition fails.

This is the main difference from while — execution always happens at least once.

Real-World Example – Password Prompt

$attempts = 0;
$password = '';

do {
    echo "Attempt #" . ++$attempts . "<br>";
    // Simulate password input
    $password = "wrong"; // change to "secret" to simulate success
} while ($password !== "secret" && $attempts < 3);

Used in login flows where the logic must run at least once regardless of input.

⛓️ Controlling Execution: break and continue

Exit Early with break

$i = 1;

do {
    if ($i == 2) break;
    echo "$i ";
    $i++;
} while ($i <= 3);

Output: 1

Exits immediately when $i == 2.

Skip Iteration with continue

$i = 0;

do {
    $i++;
    if ($i == 2) continue;
    echo "$i ";
} while ($i <= 3);

Output: 1 3

Skips printing 2.

while vs do...while Comparison

Best Practices

• Use do...while when at least one execution is required
• Set a loop limit to avoid infinite loops
• Use break and continue for better control
• Avoid complex conditions inside the while — handle them clearly above or below

Summary – Recap & Next Steps

The do...while loop is ideal when the block must run at least once, making it a unique and reliable choice for user interaction, retries, and preliminary tasks.

Key Takeaways:

• Executes once before checking the condition
• Ideal for user prompts, form validation, retries
• Use with caution to avoid infinite execution
• Can be controlled using break and continue

Real-World Use Cases:
Login attempts, polling services, user confirmation prompts, data collection loops.

Frequently Asked Questions (FAQs)

How is do...while different from while?
do...while executes once before checking the condition.

Can I break out of a do...while loop?
Yes. Use break; based on custom conditions.

Is do...while commonly used?
Less common than while, but very effective for guaranteed execution.

Can I use continue in do...while?
Yes. It skips to the condition check at the end of the loop.