PHP do…while Loop

Welcome back to The Coding College! In this tutorial, we’ll dive into the PHP do…while loop, an essential tool for situations where a block of code needs to run at least once, regardless of the condition.

What Is the PHP do…while Loop?

The do…while loop is a control structure in PHP that executes a block of code once before checking a condition. If the condition is true, the loop continues; if false, the loop stops.

This makes the do...while loop different from the while loop, where the condition is checked before the code block executes.

Syntax of do…while Loop

do {
    // Code to execute
} while (condition);

Key Features:

1. do Block: Executes the code inside the block.
2. Condition: Checked after the block is executed.
3. Guaranteed Execution: The code runs at least once, even if the condition is initially false.

Example: Basic do…while Loop

<?php
$count = 1;

do {
    echo "Count is: $count <br>";
    $count++;
} while ($count <= 5);
?>

Output:

Count is: 1  
Count is: 2  
Count is: 3  
Count is: 4  
Count is: 5  

In this example, the block runs five times because the condition $count <= 5 is true.

Difference Between while and do…while

Example Comparison

Using while:

<?php
$count = 6;

while ($count <= 5) {
    echo "Count is: $count <br>";
}
?>

Output: (No output because the condition is false.)

Using do…while:

<?php
$count = 6;

do {
    echo "Count is: $count <br>";
} while ($count <= 5);
?>

Output:

Count is: 6  

The code runs once before the condition is evaluated.

Practical Use Cases

1. Validating User Input

A do...while loop ensures the user is prompted at least once for valid input.

<?php
do {
    $input = 10; // Simulating user input
    echo "Input is $input <br>";
} while ($input < 0); // Continue only if input is negative
?>

2. Menu-Driven Applications

In CLI applications, you can use a do...while loop to present a menu until the user exits.

<?php
do {
    echo "1. Option 1 <br>";
    echo "2. Option 2 <br>";
    echo "3. Exit <br>";
    $choice = 3; // Simulate user choosing "Exit"
} while ($choice != 3);
?>

Nested do…while Loops

You can nest do...while loops for complex scenarios, such as generating tables or handling multi-step processes.

Example: Multiplication Table

<?php
$row = 1;

do {
    $col = 1;

    do {
        echo $row * $col . " ";
        $col++;
    } while ($col <= 3);

    echo "<br>";
    $row++;
} while ($row <= 3);
?>

Output:

1 2 3  
2 4 6  
3 6 9  

Breaking Out of a do…while Loop

Use the break statement to exit the loop prematurely.

Example: Breaking on a Condition

<?php
$count = 1;

do {
    echo "Count is: $count <br>";
    if ($count == 3) {
        break; // Exit the loop when count reaches 3
    }
    $count++;
} while ($count <= 5);
?>

Output:

Count is: 1  
Count is: 2  
Count is: 3  

Skipping Iterations with continue

The continue statement skips the current iteration and moves to the next one.

Example: Skipping Odd Numbers

<?php
$count = 0;

do {
    $count++;
    if ($count % 2 != 0) {
        continue; // Skip odd numbers
    }
    echo "Even number: $count <br>";
} while ($count <= 10);
?>

Output:

Even number: 2  
Even number: 4  
Even number: 6  
Even number: 8  
Even number: 10  

Common Mistakes with do…while Loops

• Infinite Loops: Ensure the condition eventually becomes false.

do {
    echo "Infinite loop!<br>";
} while (true);

• Missing Increment/Decrement: Forgetting to update variables can cause the loop to run indefinitely.

Best Practices for do…while Loops

1. Use When Execution Is Required: Only use do...while loops when you need the block to run at least once.
2. Avoid Infinite Loops: Always ensure your loop condition will eventually evaluate to false.
3. Optimize for Readability: Keep the loop logic simple to avoid confusion.

Conclusion

The do...while loop is a versatile construct in PHP, perfect for scenarios where the code block must execute at least once. By mastering it, you’ll be equipped to handle dynamic tasks efficiently.

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