The array_change_key_case() function is an inbuilt function in PHP and is used to change case of all of the keys in a given array either to lower case or upper case. Syntax:

array array_change_key_case(in_array, convert_case)

Parameters: This function accepts two parameters out of which one is mandatory and the other is optional. The two parameters are described below:

1. in_array (mandatory): This parameter refers to the array whose key's case is needed to be changed.
2. convert_case (optional): This is an optional parameter and refers to the 'case' in which we need to convert the keys of the array. This can take two values, either CASE_UPPER or CASE_LOWER. CASE_UPPER value determines the uppercase and CASE_LOWER determines lowercase. If the convert_case parameter is not passed then it's default value is taken which is CASE_LOWER.

Note: If the second parameter is ignored then by default the keys of array will get converted to lowercase. Return Type: The function returns an array with the changed case of the key, either to lowercase or to upper case. Let us now look at some programs to get a better understanding of working of array_change_key_case() function.

• Below program converts the case of keys to uppercase:
   

  <?php

  ​

  // PHP code to illustrate array_change_key_case()

  // Both the parameters are passed

  function change_case($in_array){

      return(array_change_key_case($in_array, CASE_UPPER));

  }

  ​

  // Driver Code

  $array = array("Aakash" => 90, "RagHav" => 80, 

                 "SiTa" => 95, "rohan" => 85, "RISHAV" => 70);

  print_r(change_case($array));

  ​

  ?>
  Output:

  Array
  (
      [AAKASH] => 90
      [RAGHAV] => 80
      [SITA] => 95
      [ROHAN] => 85
      [RISHAV] => 70
  )
  

• If we ignore the second parameter convert_case in the function array_change_key_case() then the keys will be converted to lowercase. Below program illustrates this:
   

  <?php

  ​

  // PHP code to illustrate array_change_key_case()

  // Second parameter is ignored

  function change_case($in_array){

      return(array_change_key_case($in_array));

  }

  ​

  // Driver Code

  $array = array("Aakash" => 90, "RagHav" => 80, 

                 "SiTa" => 95, "rohan" => 85, "RISHAV" => 70);

  print_r(change_case($array));

  ​

  ?>
  Output:

  Array
  (
      [aakash] => 90
      [raghav] => 80
      [sita] => 95
      [rohan] => 85
      [rishav] => 70
  )
  

• If we don't pass an array to the function then PHP_Warning is popped up, but the program works and No Output is generated. Below program illustrates this
   

  <?php

  ​

  // PHP code to illustrate array_change_key_case()

  // NO parameter is passed

  function change_case($in_array){

      return(array_change_key_case());

  }

  ​

  // Driver Code

  $array = array("Aakash" => 90, "RagHav" => 80, 

                 "SiTa" => 95, "rohan" => 85, "RISHAV" => 70);

  print_r(change_case($array));

  ​

  ?>
  Output:

  No Output
  

  Warning:

  PHP Warning:  array_change_key_case() expects at least 1 parameter, 
  0 given in /home/7d540b2d77cbbfa46af4fb8798fb5e79.php on line 5