How to make a calculator in PHP?

Question

I want to use PHP to calculate simple algebraic expressions like, 8*(5+1), entered via an tag by a normal user (which means,

Answer 1

There is a Math Parser class called bcParserPHP that might be of interest.

Seems fairly simple to use and pretty powerful.

Example code from their site:

$parser = new MathParser();
$parser->setVariable('X', 5);
$parser->setVariable('Y', 2);
$parser->setExpression('COS(X)+SIN(Y)/2');
echo $parser->getValue();

Unfortunately, it's a commercial product; I don't know if that would stop you using it or not (guess it depends on the price and on your needs).

A non-commercial alternative might be this one: http://www.phpclasses.org/package/2695-PHP-Safely-evaluate-mathematical-expressions.html

Note that this class uses eval() internally, which I would avoid doing if possible.

Failing that, writing your own language parser would be the ideal solution, but not really sensible to do that in PHP.