There is no built-in way to do that (except, perhaps, using the JavaScript interpreter...).
Code to evaluate such expressions abounds, from simple classes more or less complete, to commercial libraries.
You can do it yourself, but if it isn't that hard, it isn't trivial either, particularly for a beginner.

Thanks phil.ho

I think it would be worth it to create a general parser. I saw this is in an Itouch app for generating graphs and wanted to do it in processing. The app also pointed out when the equation was not structured correct due to syntax.

At first I want to just manipulate z = ????  where I can rearrange the formula other than just assigning different values to preset variables.

Example

z = a + b / t;

On the fly I want the user to type

z = a * 2 + b ^ 2 / t-2

The difference is the a becomes a *2 and b becomes b ^2 and t becomes t -2

I will stick with the basics like you said and just allow operator and value insertion for now. However I still need to evaluate it once the user hits return.


I will need a function that reads the string and returns a float value.

Thanks again.