How to add random operator from array in PHP - php

Question

I wrote this:
$num1 = mt_rand(1,5);
$num2 = mt_rand(1,5);
$operators = array(
"+",
"-",
"*",
"/"
);
$result = $num1 . $operators[array_rand($operators)] . $num2;
(My best guess is) This doesn't work as I expected because in the array the operator is a string which makes everything a string:
var_dump($result);
Gives:
string(3) "4+3"
So my question would be how would you recommend approaching this* without changing the logic it too much?
Thanks in advance!!
*Making random operation among random numbers, and if possible, the operators should be stored in an array.
I have the feeling my title is not correctly describing the situation but I could not come up with a better idea, I'm open to suggestions :)

Answer 1

Of course, you could use eval to do this, but I certainly won't settle for such a solution.
I'd suggest defining a bunch of functions that take in two params and return a result, then use call_user_func_array on the result of array_rand.
function add($x, $y) { return $x + $y; }
function subtract($x, $y) { return $x - $y; }
function multiply($x, $y) { return $x * $y; }
function divide($x, $y) { return $x / $y; }
$operators = array('add', 'subtract', 'multiply', 'divide');
//...
$result = call_user_func_array($operators[array_rand($operators)], array($x, $y));

Answer 2

<?php
$num1 = mt_rand(1, 5);
$num2 = mt_rand(1, 5);
$operators = array(
"+",
"-",
"*",
"/"
);
switch ($operators[array_rand($operators)]) {
case "+":
$result = $num1 + $num2;
break;
case "-":
$result = $num1 - $num2;
break;
case "*":
$result = $num1 * $num2;
break;
case "/":
$result = $num1 / $num2;
break;
}
var_dump($result);

Answer 3

The clean solution would be to have a code branch for each operator, e.g.
function do_something($num1, $num2, $operator) {
switch ($operator) {
case '+':
return $num1 + $num2;
case '-':
return $num1 - $num2;
case '*':
return $num1 * $num2;
case '/':
return $num1 / $num2;
default:
throw new Exception('Unknown operator: '.$operator)
}
}
If you have more operators, you should create a map of operator => function and dynamically call the functions, for example:
$ftable = array(
'+' => 'fn_add',
'-' => 'fn_sub',
'*' => 'fn_mul',
'/' => 'fn_div'
);
function fn_add($a, $b) { return $a + $b; }
function fn_sub($a, $b) { return $a - $b; }
function fn_mul($a, $b) { return $a * $b; }
function fn_div($a, $b) { return $a / $b; }
function do_something($num1, $num2, $operator) {
global $ftable;
if (array_key_exists($operator, $ftable)) {
return call_user_func($ftable[$operator], $num1, $num2);
}
else {
throw new Exception('Unknown operator: '.$operator)
}
}
And of course, the unclean (slow, potentially dangerous) solution would be to use eval().

Answer 4

Create a function for each operation, then store operator => function name in an array.