Index_Number

if you use the array_push() function to add a new item, the new item will get the index 3:

        array(4) {
  [0]=>
  string(5) "Volvo"
  [1]=>
  string(3) "BMW"
  [2]=>
  string(6) "Toyota"
  [3]=>
  string(4) "Ford"
}