PHP Loops

<?php
// Standard counter
for ($i = 0; $i < 5; $i++) {
    echo $i . " ";        // 0 1 2 3 4
}

// Count backwards
for ($i = 10; $i >= 1; $i--) {
    echo $i . " ";        // 10 9 8 7 ... 1
}

// Step by 2
for ($i = 0; $i <= 20; $i += 2) {
    echo $i . " ";        // 0 2 4 ... 20
}

// Multiple counters
for ($i = 0, $j = 100; $i < 5; $i++, $j -= 10) {
    echo "$i:$j ";
}

<?php
$colors = ["red", "green", "blue"];

// Value only
foreach ($colors as $color) {
    echo $color . "\n";
}

// Key + value
foreach ($colors as $index => $color) {
    echo "$index: $color\n";
}

// Associative
$user = ["name" => "Ruban", "age" => 30];
foreach ($user as $field => $value) {
    echo "$field = $value\n";
}

// By reference - modify in place
foreach ($colors as &$color) {
    $color = strtoupper($color);
}
unset($color);   // critical!

// Destructure values inline (PHP 7.1+)
$users = [["alice", 30], ["bob", 25]];
foreach ($users as [$name, $age]) {
    echo "$name is $age\n";
}

<?php
$i = 0;
while ($i < 5) {
    echo $i . " ";
    $i++;
}

// Reading lines from a file
$fh = fopen("data.txt", "r");
while (($line = fgets($fh)) !== false) {
    echo $line;
}
fclose($fh);

// Reading database rows
while ($row = $stmt->fetch()) {
    process($row);
}

<?php
// Prompt until user enters valid input
do {
    $answer = readline("Continue? (y/n): ");
} while ($answer !== "y" && $answer !== "n");

// Retry with exponential backoff
$attempt = 0;
$result  = null;
do {
    $result = tryRequest();
    if ($result !== null) break;
    sleep(2 ** $attempt);
    $attempt++;
} while ($attempt < 5);

<?php
// break - exit the loop entirely
foreach ($users as $user) {
    if ($user->isBanned()) {
        echo "Banned user found, stopping";
        break;
    }
    sendEmail($user);
}

// continue - skip to next iteration
foreach ($numbers as $n) {
    if ($n < 0) continue;     // skip negatives
    echo sqrt($n) . "\n";
}

// break N - exit nested loops
foreach ($categories as $cat) {
    foreach ($cat->items as $item) {
        if ($item->id === $needle) {
            $found = $item;
            break 2;          // exit BOTH loops
        }
    }
}

<?php
// Print a multiplication table
for ($row = 1; $row <= 5; $row++) {
    for ($col = 1; $col <= 5; $col++) {
        printf("%4d", $row * $col);
    }
    echo "\n";
}

// Walk a 2D grid
foreach ($grid as $y => $row) {
    foreach ($row as $x => $cell) {
        if ($cell === "*") echo "Found at ($x, $y)\n";
    }
}