How to calc with operations in variable

Question

is there a way in PHP to calc if the operations are in variables as strings? Like this:

<?php
    $number1=5;
    $number2=10;
    $operations="+";

    $result = $number1 . $operations . $number2;
?>

I get it, this is just an example, but still... `number1=5` -> `$number1=5;` — domsson, Jun 30 '17 at 08:26

RJParikh · Answer 1 · 2017-06-30T09:06:16.220

2

Use eval().

Note: Avoid eval() It is not safe. Its Potential unsafe.

<?php

$number1=5;
$number2=10;
$operations="+";

$result= $number1.$operations.$number2;

echo eval("echo $result;");

Output

Demo: Click Here

edited Jun 30 '17 at 09:06

answered Jun 30 '17 at 08:30

RJParikh

4,096
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ty, didn't knew about eval – DrSheldonTrooper Jun 30 '17 at 08:36
1

eval() is not safe. https://stackoverflow.com/questions/951373/when-is-eval-evil-in-php – Companjo Jun 30 '17 at 08:39
Yes but as per questioner requirement I am helping. @Companjo – RJParikh Jun 30 '17 at 08:45
@RJParikh i understand, but it's better to inform him about the security risks too. Beside that, a switch is a better and safe alternative. – Companjo Jun 30 '17 at 08:55
Ok, I forgot it. I have added note. @Companjo – RJParikh Jun 30 '17 at 09:06

score 2 · Accepted Answer · answered Jun 30 '17 at 08:37

2

Assuming that the code you've given is a pseudo-code...

Given you have a limited set of operations that can be used, you can use switch case.

Using eval() can be a security issue if you are using user input for it...

A switch case example would be:

<?php

$operations = [
    '+' => "add",
    '-' => "subtract"
];

// The numbers
$n1 = 6;
$n2 = 3;
// Your operation
$op = "+";

switch($operations[$op]) {
    case "add":
        // add the nos
        echo $n1 + $n2;
        break;
    case "subtract":
        // subtract the nos
        echo $n1 - $n2;
        break;
    default:
        // we can't handle other operators
        throw new RuntimeException();
        break;
}

In action

answered Jun 30 '17 at 08:37

Ikari

3,176
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yeah I did it like this before but I work with a user input and i dont want to create to many switch cases or ifs – DrSheldonTrooper Jun 30 '17 at 08:43
yeah... so if you are processing user input, you SHOULD NEVER use eval... – Ikari Jun 30 '17 at 08:46
2

@DrSheldonTrooper don't use eval() when processing user input. Use a switch instead. Here an explanation about eval() https://stackoverflow.com/questions/951373/when-is-eval-evil-in-php – Companjo Jun 30 '17 at 09:23

How to calc with operations in variable

2 Answers2