Convert form's string variable to numeric?

Hi ppl,
When I send via form to script the "4+4" expression script got it as string variable.
Is there any way to convert form's string variable to numeric variable?

P.S.
Don't tell me to use with intval() function cause:

$string="4+4"; /*For experiment*/
$var=intval($string);
print $var; /* Print: 4, cause for intval() "+" is not valid charecter*/

How about this:

<?
$string="4+4";
$total=intval($string[0]) + intval($string[2]);
print $total;
?>

of course that only works with one digit numbers...try this for something that works with bigger numbers:

<?
$string="4+4";
$strings = explode('+',$string);
$total=intval($strings[0]) + intval($strings[1]);
print $total;
?>

I found better solution:

$str = "4+4";
eval("$var = $str;");
print $var;

Somthing wrong with your forum:
I tried to post:
eval("$var = $str;");

*Slash disappear before $var!

try using three slashes - you escape the quotes and then escape the escape character...
for example

"$var"