guys this is a simple question for most of you probably. but im confused on how can i perform operations with operator symbol saved in a variable. Example.
$first=5; $second=5; $operator="+"; $result=$first.$operator.$second; echo $result; but $result will just print 5+5. i want it to perform the operation.
my idea is to put it all operations in an if condition -> if($operator == '+'){add the first and second operand}. any other ideas guys?
Instead of using eval(), you may try a custom function with a switch() inside:
$first = 5; $second = 3; $operator = '+'; $result = mathOp($operator, $first, $second); echo $result; function mathOp($operator, $n1, $n2){ if(!is_numeric($n1) || !is_numeric($n2)){ return 'Error: You must use numbers'; } switch($operator){ case '+': return($n1 + $n2); case '-': return($n1 - $n2); case '*': return($n1 * $n2); case '/': if($n2 == 0){ return 'Error: Division by zero'; }else{ return($n1 / $n2); } default: return 'Unknown Operator detected'; } } 
You have to use eval() which executes a PHP operation.
$first=5; $second=5; $operator="+"; $term = $first.$operator.$second; eval("$result = " . $term); echo $result; But be careful with eval it executes every PHP function. (Even exec..)
if(in_array($operator, array('+', '-', '*', '/', '%'))) then execute the eval functionEval is one solution, but there are others. If your search SO for math parser, you will find many answers. This one is a good example.
So basically, your choices are: eval() with some validation first, or a custom math parser that does it for you, such as evalMath.
If your are looking only for simple operations (+, -, *, /) and two operators, use a validation function for your parameters (numbers only, known operators only) and use eval. If your want to be able to parse complex operations (parenthesis, variables...) then go with a parser.
You are not far off with your own syntax, when you use
$first.$operator.$second; You are literally adding the strings together, you need to use the '+' operator to successfully use your method. See below code, tried and tested
$first = 5; $second = 5; $operator = '+'; $result = $first+$operator+$second; echo $result; ?> 
$result = $first+$operator+$second; PHP checks the value of $first which is 5, then PHP checks the value of $operator, but oops it's a string, so PHP converts it to a number which is 0 echo intval('+');, and then PHP checks $second which is 5 so the equation becomes 5+0+5 = 10. So for example if you do $operator = '*'; It will always return 10.
eval(). That's usually an indicator that you should be doing something different. I suggest reviewing your strategy.