- array_unshift: documentation ( source)
- print_r: documentation ( source)
<?php
$a = array(100=>'a',200=>'b',300=>'c',400=>'d');
array_unshift($a,'z');
print_R($a);
// What you have to do
$a = array(100=>'a',200=>'b',300=>'c',400=>'d');
$a = array(0=>'z') + $a;
print_R($a);