Calculate formula to double

What you are trying to do is an Excel style formula... what Excel doesn't tell you is that there is a lot of work done behind the scenes to make "=2+1" into a valid mathematical statement. If you want to do this in C#, you will have to recreate that type of logic in your application. This means you will have to parse the string character by character, determine what type of calculation it is, extract the numbers and then perform the equation to give yourself the proper answer. Sorry to be the bearer of bad news