phpapprentice/chapters/loops.md

A loop tells PHP to run a block of code more than once. A classic loop is a while loop. A "while" loop will continue to run the block of code as long as the value in parentheses is true.

<?php

$num = 5;
while ($num > 0) {
    echo "While loop $num\n";
    --$num;
}

A "do while" loop is similar to a "while" loop except it always runs at least one iteration. In a classic "while" loop, no iterations may be executed if the value in parentheses is false. In a "do while", the boolean check is not done until after the execution of an iteration.

$num = 0;
do {
    echo "Do while $num\n";
    ++$num;
} while ($num < 5);

"for" loops allow you to create a more concise while loop. Inside the parentheses, the left section creates a variable before the loop starts, the middle section is the check that is done at the beginning of each loop and the third section is executed after each loop.

for ($i = 0; $i < 10; $i++) {
    echo "For loop $i\n";
}

A "foreach" loop allows you to easily loop over an array. An array is a list of data stored together. The "as" keyword lets you assign a variable to the value in the array for the current iteration of the loop.

$set = [1, 2, 3, 4, 5];
foreach ($set as $num) {
    echo "Array value $num\n";
}

In loops, you can use the keyword "break" to stop the loop execution no matter how many more iterations should run.

$values = ['one', 'two', 'three'];
foreach ($values as $value) {
    if ($value === 'two') {
        break;
    }
    echo "Break $value\n";
}

The "continue" keyword stops executing the current loop iteration, but then allows the loop to continue with other iterations.

$values = ['one', 'skip', 'three'];
foreach ($values as $value) {
    if ($value === 'skip') {
        continue;
    }
    echo "Continue $value\n";
}