We have given an array arr and a Key key, the task is to check if a key exists in an array or not in PHP.

Examples:

Input : arr = [“Devop1”, “Devop2”, “1”, “2”,”3″]
key = “2”
Output: Found the Key

Input : arr = [“Devop1”, “Devop2”, “1”, “2”,”3″]
key = 9
Output: Key not Found

The problem can be solved using PHP inbuilt function for checking key exists in a given array. The in-built function used for the given problem are:

Method 1: Using array_key_exists() Method: The array_key_exists() function checks whether a specific key or index is present inside an array or not.

Syntax:

boolean array_key_exists( $index, $array )
Example:

<?php
// PHP program to check if a key 
// exists in an array or not
  
$array = array(
      'names' => array("Devop1", "Devop2", "Devop3"), 
    'rank' => array('1', '2', '3')
); 
  
// Use of array_key_exists() function
if(array_key_exists("rank", $array)) {
    echo "Found the Key"; 
} 
else{ 
    echo "Key not Found"; 
} 
  
?>

Output
Found the Key
Method 2: Using isset() Method: The isset() function checks whether a specific key or index is present inside an array or not.

Syntax:

bool isset( mixed $var, mixed $… )

<?php
// PHP program to check if a key 
// exists in an array or not
  
$array = array(
      'names' => array("Devop1", "Devop2", "Devop3"), 
    'rank' => array('1', '2', '3')
); 
  
// Use of array_key_exists() function
if(isset($array["rank"])){
    echo "Found the Key"; 
} 
else{ 
    echo "Key not Found"; 
} 
  
?>

Output
Found the Key