The while loop in PHP is a basic control structure that repeats a block of code as long as a logical condition is true. It is especially useful when:

you don’t know in advance how many times the code should run (unknown number of iterations),
you read data from a stream (file, database, user input),
you wait for a condition to be met (data arrival, process completion).

In PHP programming, the while loop is a foundation alongside for and foreach. It allows you to write clean, concise code and solve real-world problems: from simple counters to iterating over database query results.

Basics: how does while work in PHP

Syntax of the while loop

The loop checks the condition at the beginning of each iteration.
If the condition is true, it executes the block and returns to check again.
If the condition is false, the loop ends.

<?php
while (condition) {
    // code executed as long as condition is true
}

Typically:

variables are initialized before the loop,
variables are updated inside the loop so that the condition eventually becomes false.

Comparison: while vs for vs foreach

while: best when the number of iterations is unknown (files, DB records).
for: convenient when the counter and iteration count are known (1 to 10).
foreach: preferred for arrays/collections (clearer than while in that context).

Variation: the do-while loop

do-while executes the block at least once, checking the condition only after the first pass.
Useful when you need to run something once (e.g., display a menu) and maybe repeat.

<?php
do {
    // code runs at least once
} while (condition);

PHP Code Examples (with comments)

1) Counting up

<?php
$i = 1;
while ($i <= 5) {
    echo $i . PHP_EOL;
    $i++;
}
// Output: 1 2 3 4 5

2) Counting down

<?php
$i = 5;
while ($i > 0) {
    echo $i . ' ';
    $i--;
}
// Output: 5 4 3 2 1

3) Summing numbers until 0 (CLI)

<?php
$sum = 0;

echo "Enter integers (0 to stop):" . PHP_EOL;

while (true) {
    $line = fgets(STDIN);
    if ($line === false) break; // end of input (CTRL+D)

    $line = trim($line);
    if ($line === '') continue; // skip empty lines

    $num = (int) $line;
    if ($num === 0) break; // exit condition

    $sum += $num;
}

echo "Sum: {$sum}" . PHP_EOL;

4) while with break and continue

<?php
$i = 0;
while ($i < 10) {
    $i++;

    if ($i % 2 === 0) continue; // skip even
    if ($i > 7) break;          // stop when >7

    echo $i . ' ';
}
// Output: 1 3 5 7

5) Using array as a queue

<?php
$queue = ['task1', 'task2', 'task3'];

while (!empty($queue)) {
    $task = array_shift($queue);
    echo "Processing: {$task}" . PHP_EOL;
}

6) Reading a file line by line

<?php
$path = __DIR__ . '/data.txt';
$handle = fopen($path, 'r');
if ($handle === false) die("Cannot open file: {$path}");

while (($line = fgets($handle)) !== false) {
    echo strtoupper($line);
}

if (!feof($handle)) {
    fwrite(STDERR, "File read error." . PHP_EOL);
}

fclose($handle);

Avoid the bad pattern while (!feof($h)) { $line = fgets($h); ... } — may duplicate or misread the last line.

7) Iterating DB results (PDO)

<?php
$pdo = new PDO(
    'mysql:host=localhost;dbname=app;charset=utf8mb4',
    'user',
    'pass',
    [PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION]
);

$stmt = $pdo->query('SELECT id, name FROM users');
while ($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    echo $row['id'] . ': ' . $row['name'] . PHP_EOL;
}

8) do-while executes at least once

<?php
$i = 10;
do {
    echo "Value of i: {$i}" . PHP_EOL;
    $i++;
} while ($i < 5);

9) Nested while – multiplication table 1–3

<?php
$i = 1;
while ($i <= 3) {
    $j = 1;
    while ($j <= 3) {
        echo ($i * $j) . ' ';
        $j++;
    }
    echo PHP_EOL;
    $i++;
}

10) Infinite loop with time limit

<?php
$start = microtime(true);
$timeout = 3.0;

while (true) {
    if (microtime(true) - $start >= $timeout) break;
    usleep(200_000);
}

Best Practices and Common Mistakes

Best Practices

Always initialize variables before the loop.
Ensure condition updates inside the loop.
Always use braces { } even for single statements.
Prefer foreach for arrays; while fits unknown-length tasks (streams, queues, cursors).
In while(true), always add break conditions and time/iteration limits.
Use safe patterns for I/O (strict checks like !== false).
Limit expensive I/O (echo/print) in long loops.

Common Mistakes

Forgetting to update variables → infinite loop.
Using continue before increment → stuck loop.
Wrong file read pattern with feof.
Off-by-one errors (< vs <=).
Using floats in conditions.
Using while for arrays instead of foreach.
Long loops in web context without limits → timeout risk.

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Summary

while runs code as long as the condition is true.
Best for unknown iteration count: streams, files, DB cursors.
Remember to init and update variables + exit conditions.
Use foreach for arrays.
Avoid pitfalls: infinite loops, bad file reads, float conditions.

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Mini Quiz

Output?

$i = 1;
while ($i <= 3) {
    echo $i;
    $i++;
}

➡️ 123

True/false:

A. while checks before execution. (true)

B. do-while checks after execution. (true)
C. do-while may not run at all. (false)
D. while always runs at least once. (false)

Find bug:

$i = 0;
while ($i < 5) {
    if ($i % 2 === 0) {
        continue;
    }
    echo $i;
    $i++;
}

➡️ Infinite loop (i not updated on continue).

Correct file read pattern?

➡️ while (($line = fgets($h)) !== false) { ... }

Best for array iteration? ➡️ foreach

Output?

$count = 0;
while (true) {
    $count++;
    if ($count === 3) break;
}
echo $count;

➡️ 3

Good practice? ➡️ Add time/iteration limit to while(true).

Difference while vs for? ➡️ while: unknown iterations, for: known counter/iterations.

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Now you know how to use the while and do-while loops in PHP to handle unknown-length tasks like reading files, processing queues, or iterating DB results.