array_walk(): applies a user-defined callback function to each element in an array

array_walk(input_array, function, optional_extra_parameter )

Return Value ( boolean ): TRUE on success or FALSE on failure

<?Php
function add_char($str){
$str = $str.'x';
echo $str.'<br>';
}
$a= array(1,2,v,4,7.3,105 ); 

array_walk($a, 'add_char');
?>

1x
2x
vx
4x
7.3x
105x

<?Php
function add_char($str){
$str = $str.'x';
echo $str.'<br>';
}
$a= array(1,2,v,4,7.3,105 ); 

if(array_walk($a, 'add_char')){
echo " Success ";
}else{
echo " Failed";
}
?>

1x
2x
vx
4x
7.3x
105x
Success

array_walk with optional parameter

function my_function(&$value,$key,$v1){
$value=$value*$v1;
}

$a= array('First'=>1,'Second'=>2,'Third'=>3 ); 

if(array_walk($a, 'my_function',2)){
echo "  Success <br> ";
}else{
echo " Failed <br>";
}
print_r($a);

Success
Array ( [First] => 2 [Second] => 4 [Third] => 6 )

Example : Using `array_walk()` to Transform Array Data

This example demonstrates modifying each element in an array using array_walk() to format data. Here, we append a unit to each numeric value.

<?php
$prices = [100, 200, 300];
array_walk($prices, function(&$value) {
    $value = "$" . $value . ".00";  // Append currency format
});
print_r($prices);
?>

Output:

Array ( [0] => $100.00 [1] => $200.00 [2] => $300.00 )

Difference between array_map and array_walk

Read more on array_map()