how to change the array key to start from 1 instead of 0

Here is my suggestion:

<?php
$alphabet = array(1 => 'a', 'b', 'c', 'd');
echo '<pre>';
print_r($alphabet);
echo '</pre>';
?>

The above example will output:

Array
(
    [1] => a
    [2] => b
    [3] => c
    [4] => d
)

Simply try this

$array = array("a","b","c");
array_unshift($array,"");
unset($array[0]);

$alphabet = array("a", "b", "c");
array_unshift($alphabet, "phoney");
unset($alphabet[0]);

Edit: I decided to benchmark this solution vs. others posed in this topic. Here's the very simple code I used:

$start = microtime(1);
for ($a = 0; $a < 1000; ++$a) {
    $alphabet = array("a", "b", "c");
    array_unshift($alphabet, "phoney");
    unset($alphabet[0]);
}
echo (microtime(1) - $start) . "\n";


$start = microtime(1);
for ($a = 0; $a < 1000; ++$a) {
    $stack = array('a', 'b', 'c');
    $i= 1;
    $stack2 = array();
    foreach($stack as $value){
        $stack2[$i] = $value;
        $i++;
    }
    $stack = $stack2;
}
echo (microtime(1) - $start) . "\n";


$start = microtime(1);
for ($a = 0; $a < 1000; ++$a) {
    $array = array('a','b','c');

    $array = array_combine(
        array_map(function($a){
            return $a + 1;
        }, array_keys($array)),
        array_values($array)
    );
}
echo (microtime(1) - $start) . "\n";

And the output:

0.0018711090087891
0.0021598339080811
0.0075368881225586