PHP while Loop : A Tutorial with Examples

The while loop in PHP is one of the basic control structures used for repeating a block of code as long as a specified condition remains true.

It is particularly useful when the number of iterations is unknown, and the loop needs to continue until a condition is met.

In this tutorial, we will cover:

Let’s explore each of these concepts with examples and explanations.

1. What is a while Loop?

A while loop in PHP is used to execute a block of code repeatedly as long as the specified condition evaluates to true.

It is commonly used when you do not know how many times the loop should run in advance, and the loop needs to keep running until a specific condition changes.

Key Points:

• The condition is evaluated before each iteration of the loop.
• If the condition is false from the beginning, the loop will not execute at all.
• It’s important to update the condition inside the loop to avoid infinite loops.

2. Basic Syntax of while Loop

Syntax:

while (condition) {
    // Code to execute as long as the condition is true
}

• condition: The expression that is evaluated before each iteration. If the condition is true, the loop continues; if it’s false, the loop stops.

3. How the while Loop Works

1. Evaluate the condition: Before each iteration, PHP checks the condition.
2. If the condition is true, the block of code inside the loop is executed.
3. If the condition is false, the loop terminates, and the program moves to the next statement after the loop.
4. The condition is re-evaluated before every iteration.

4. Examples of Using the while Loop

Example 1: Simple while Loop

<?php
$count = 1;

while ($count <= 5) {
    echo "Count: $count\n";
    $count++;
}
?>

Output:

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

• In this example, the while loop continues running as long as $count is less than or equal to 5. After each iteration, the value of $count is incremented by 1.

Example 2: Loop with User Input

<?php
$number = 0;

// Continue to ask the user for input until a positive number is entered
while ($number <= 0) {
    $number = (int) readline("Enter a positive number: ");
}

echo "You entered a positive number: $number\n";
?>

• In this example, the loop will repeatedly ask the user for input until they enter a positive number.

5. Common Pitfalls: Infinite Loops

An infinite loop occurs when the condition of a while loop never becomes false.

This can cause your program to run indefinitely. To avoid infinite loops, ensure that the condition will eventually become false during the loop execution.

Example (Infinite Loop):

<?php
$count = 1;

while ($count <= 5) {
    echo "Count: $count\n";
    // Oops! Forgot to increment $count
}
?>

• In this example, the loop will run indefinitely because the value of $count never changes. To fix this, you need to increment $count inside the loop.

Example (Fixed Loop):

<?php
$count = 1;

while ($count <= 5) {
    echo "Count: $count\n";
    $count++;  // Increment to avoid infinite loop
}
?>

• This version correctly increments $count, ensuring that the loop eventually ends when $count exceeds 5.

6. Using the break and continue Statements in while Loops

break Statement:

The break statement is used to exit the loop early. When break is encountered, the loop terminates immediately, regardless of the condition.

Example (Using break in a while Loop):

<?php
$count = 1;

while (true) {  // Infinite loop, but we will use break
    echo "Count: $count\n";
    
    if ($count >= 3) {
        break;  // Exit the loop when count reaches 3
    }
    
    $count++;
}
?>

Output:

Count: 1
Count: 2
Count: 3

• In this example, the loop would run infinitely because the condition is true, but the break statement is used to stop the loop when $count reaches 3.

continue Statement:

The continue statement skips the remaining code in the current iteration and proceeds to the next iteration of the loop.

Example (Using continue in a while Loop):

<?php
$count = 0;

while ($count < 5) {
    $count++;

    if ($count == 3) {
        continue;  // Skip the rest of this iteration when count is 3
    }

    echo "Count: $count\n";
}
?>

Output:

Count: 1
Count: 2
Count: 4
Count: 5

• In this example, when $count equals 3, the continue statement skips the echo statement and moves to the next iteration, effectively skipping the number 3 in the output.

7. Do-While Loop

PHP also provides a do-while loop, which is similar to a while loop but guarantees that the loop runs at least once. In a do-while loop, the condition is checked after the code inside the loop has executed.

Syntax:

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

Example (Do-While Loop):

<?php
$count = 6;

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

Output:

Count: 6

• In this example, the code inside the do-while loop runs once even though the condition is false ($count is already greater than 5). This demonstrates that the code block in a do-while loop is executed at least once.

Summary of PHP while Loop:

Conclusion

The while loop in PHP is a powerful tool for repeating a block of code based on a condition.

It’s commonly used when the number of iterations is not known in advance.

In this tutorial, we covered:

• The syntax of the while loop and how it works.
• Examples of using the while loop with different data types and scenarios.
• How to avoid infinite loops by ensuring the condition is updated.
• Using the break and continue statements to control loop execution.
• The do-while loop, which guarantees at least one execution of the loop body.