This built-in function of PHP is used to exchange elements within an array, i.e., exchange all keys with their associated values in an array and vice-versa. We must remember that the values of the array need to be valid keys, i.e. they need to be either integer or string. A warning will be thrown if a value has the wrong type, and the key/value pair in question will not be included in the result.
Input : array = ("aakash" => 20, "rishav" => 40, "gaurav" => 60) Output: Array (  => aakash  => rishav  => gaurav ) Explanation: The keys and values are exchanged and the last key or value is taken. Input : array = ("aakash" => "rani", "rishav" => "sristi", "gaurav" => "riya", "laxman" => "rani") Output: Array ( [rani] => laxman [sristi] => rishav [riya] => gaurav )
Parameters: The function takes only one parameter $array that refers to the input array.
Return Type: This function returns another array, with the elements exchanged or flipped, it returns null if the input array is invalid.
Below program illustrates the working of array_flip() function in PHP:
Array ( [rani] => laxman [sristi] => rishav [riya] => gaurav )
If multiple values in the array are the same, then on the use of the array_flip() function, only the key with the maximum index (after swap) will be added to the array. (This is done to ensure that no keys have duplicates.)
Array (  => b  => c )