Calculating with Operator Inside Variable?

[chaseman]

I'm trying to build a math game.

 

But I'm having trouble trying to make a variable calculate that contains an operator.

 

Example:

 

$c1_op = "+";
$a1_num_user = $_POST['a1_num'];
$e1_num_user = $_POST['e3_num'];

$row_1 = $a1_num_user . $c1_op . $e1_num_user;
echo "result: " . $row_1;

 

If I now input a 10 and a 2 I will get echo'd out:

 

result: 10+2

 

It's not calculating. When I don't use any quotation marks then I will get the error "unexpected ;".

 

I need the operator inside a variable, it's the nature of the math game, any idea how I can make it work so it calculates?

[AbraCadaver]

$row_1 = eval("return $a1_num_user $c1_op $e1_num_user;");

[.josh]

okay so there are a couple ways to go about this.  One is by making use of eval() as AC has shown.  I don't really recommended doing this because it opens up for a lot of potential security issues.  eval() executes whatever string you pass it as php code.  So the user can enter in php code and eval will execute it. 

 

One alternative to setup a condition like so:

 

$c1_op = "+";
$a1_num_user = $_POST['a1_num'];
$e1_num_user = $_POST['e3_num'];

switch($c1_op) {
  case '+' : $row_1 = $a1_num_user + $e1_num_user; break;
  case '-' : $row_1 = $a1_num_user - $e1_num_user; break;
  // etc...
}

echo "result: " . $row_1;

 

 

[chaseman]

Every time eval comes up I think of evil because people mention the security issues 

 

 

Your case example worked great though, thanks a lot.