PHP String Calculation

Question

My question is,

How can we separate out digits and operators from a string in PHP?

Eg - What is 2 + 2?

So, how can we take the 2 + 2 out from that string, CALCULATE it, and display the appropriate result?

Thanks.

Answer 1

function calculate_string( $mathString )    {
    $mathString = trim($mathString);     // trim white spaces
    $mathString = ereg_replace ('[^0-9\+-\*\/\(\) ]', '', $mathString); 

    $compute = create_function("", "return (" . $mathString . ");" );
    return 0 + $compute();
}

$string = " (1 + 1) * (2 + 2)";
echo calculate_string($string);

Answer 2

Take a look at the evalMath class on PHPClasses, which can handle quite complex formulae.

Alternatively:

$string = '2 + 2';
list($operand1,$operator,$operand2) = sscanf($string,'%d %[+\-*/] %d');
switch($operator) {
    case '+' :
        $result = $operand1 + $operand2;
        break;
    case '-' :
        $result = $operand1 - $operand2;
        break;
    case '*' :
        $result = $operand1 * $operand2;
        break;
    case '/' :
        $result = $operand1 / $operand2;
        break;
}
echo $result;

Answer 3

If you want to calculate something that does not take into account grouping operators (such as ( and ) ) or follow the order of operations / operator precedence, this is a fairly straightforward.

If however you do want to take those things into account, then you have to be willing to write a parser for a context free language.

OR, you could search for a library out there that has already been written