String in between an array?

ok so I have 开发者_StackOverflow社区an array with an unknown array amount.

so like it can be

$array[0] = "a"
$array[1] = "b"
$array[2] = "c"

and what I want is the possibility to make an extra array in between each one, so like

$array[0] = "a"
$array[1] = "1"
$array[2] = "b"
$array[3] = "1"
$array[4] = "c"
$array[5] = "1"

<?php
function stringInBetweenArray($arr, $str){         
        $returnArray = array();
        foreach($arr as $item){
                $returnArray[] = $item;
                $returnArray[] = $str;
        }   
        return $returnArray;
}

$array = array("a", "b", "c");    
print_r(stringInBetweenArray($array, "1"));    
?>

Psuedocode:

new_array = new array(old_array_length * 2)
foreach (index, value) in old_array
    new_array[index * 2] = value;
    new_array[index * 2 + 1] = new_value;
return new_array