PHP building a basic calculator system from user input.

Question

I'd like to make a script where the user can enter a sum e.g. 4^5+(56+2)/3 or any other basic maths sum (no functions etc.) how would I go about doing this? Presumably regex. Could somebody point me in the right direction - I'm guessing this isn't going to be too easy so I'd just like some advice on where to start and I'll take it from there.

Answer 1

Have a look at this: http://www.webcheatsheet.com/php/regular_expressions.php

It's a good intro to Regular Expressions and how to use them in PHP.

Yes, someone can (and probably will) just give you the regex you need to work this out but it helps a lot if you understand HOW your regex works. They look scary but aren't that bad really...

Answer 2

Hi,this is not my code, but there is a great PHP snippet that lets you use Google Calculator to do the calculations. So you can just enter your query (ie, "7+3") using regular/FOIL notation or whatever, and it will return the result.

http://www.hawkee.com/snippet/5812/

<?php

// Google calculator
function do_calculator($query){
    if (!empty($query)){
        $url = "http://www.google.co.uk/search?q=".urlencode($query);
        $f = array("Â", "<font size=-2> </font>", " &#215; 10", "<sup>", "</sup>");$t = array("", "", "e", "^", "");
        preg_match('/<h2 class=r style="font-size:138%"><b>(.*?)<\/b><\/h2>/', file_get_contents($url), $matches);
        if (!$matches['1']){
            return 'Your input could not be processed..';
        } else {
            return str_replace($f, $t, $matches['1']);
        }
    } else {
        return 'You must supply a query.';
        }
    }

?>

Answer 3

The easy way to do it is with eval(). If you're accepting arbitrary input from a web form and executing in on a server, though, you MUST be careful to only accept valid expressions. Use a regex for that.