php check to see if variable is integer

Is there a nicer way to do this?

if( $_POST['id'] != (integer)$_POST['id'] )
    echo 'not a integer';

I've tried

if( !is_int($_POST['id']) )

But is_int() doesn't work for some reason.

My form looks like this

<form method="post">
   <input type="text" name="id">
</form>

I've researched is_int(), and it seems that if

is_int('23'); // would return false (not what I want)
is_int(23);   // would return true

I've also tried is_numeric()

is_numeric('23'); // return true
is_numeric(23); // return true
is_numeric('23.3'); // also returns true (not what I want)

it seems that the only way to do this is: [this is a bad way, do not do it, see note below]

if( '23' == (integer)'23' ) // return true
if( 23 == (integer)23 ) // return true
if( 23.3 == (integer)23.3 ) // return false
if( '23.3' == (integer)'23.3') // return false

But is there a function to do the above ?

---

Just to clarify, I want the following results

23     // return true
'23'   // return true
22.3   // return false
'23.3' // return false

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Note: I just figured out my previous solution that I presented will return true for all strings. (thanks redreggae)

$var = 'hello';
if( $var != (integer)$var )
    echo 'not a integer';

// will return true! So this doesn't work either.

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This is not a duplicate of Checking if a variable is an integer in PHP, because my requirements/definitions of integer is different than theres.