in_array??

[nikko50]

How can I see if something exists in an array?? I keep getting an error...
Warning: Wrong datatype for second argument in call to in_array

$check_state is an array that returns the below when printed.
Array ( [0] => 757 [1] => 758 [2] => 759 [3] => 760 [4] => 761 [5] => 762 [6] => 763 )

If(in_array($list[$key], $check_state)){

                      $check_answer="YES";
                     } Else {
                       $check_answer="";
                       }

[ClarkF1]

I tried creating the array and then searching the array for one of the values using

in_array('757', $check_state) and got the answer "YES"

What data type is $list[$key]???