4.5.1. Problem

4.5.2. Solution

foreach ($array as $value) {
    // Act on $value
}

Or, to get an array's keys and values:

foreach ($array as $key => $value) {
    // Act II
}

for ($key = 0, $size = count($array); $key < $size; $key++) {
   // Act III
}

reset($array) // reset internal pointer to beginning of array
while (list($key, $value) = each ($array)) {
    // Final Act
}

4.5.3. Discussion

A foreach loop is the shortest way to iterate through an array:

// foreach with values
foreach ($items as $cost) {
    ...
}

// foreach with keys and values
foreach($items as $item => $cost) {
    ...
}

With foreach, PHP iterates over a copy of the array instead of the actual array. In contrast, when using each( ) and for, PHP iterates over the original array. So, if you modify the array inside the loop, you may (or may not) get the behavior you expect.

If you want to modify the array, reference it directly:

reset($items);
while (list($item, $cost) = each($items)) {
    if (! in_stock($item)) { 
        unset($items[$item]);           // address the array directly
    }
}

The variables returned by each( ) aren't aliases for the original values in the array: they're copies, so, if you modify them, it's not reflected in the array. That's why you need to modify $items[$item] instead of $item.

for ($item = 0, $size = count($items); $item < $size; $item++) {
    ...
}

If you prefer to count efficiently with one variable, count backwards:

for ($item = count($items) - 1; $item >= 0; $item--) {
    ...
}

for (reset($array); $key = key($array); next($array) ) {
    ...
}

This fails if any element holds a string that evaluates to false, so a perfectly normal value such as 0 causes the loop to end early.

// lowercase all words
$lc = array_map('strtolower', $words);

The first argument to array_map( ) is a function to modify an individual element, and the second is the array to be iterated through.

if (is_array($items)) {
    // foreach loop code for array
} else {
    // code for scalar
}

settype($items, 'array');
// loop code for arrays

This turns a scalar value into a one element array and cleans up your code at the expense of a little overhead.

4.5.4. See Also