Evaluating List<String> as a mathematical expression

Question

I have a List<String> that is full of values and operators.

["123", "+", "(", "890", "-", "15.00", ")"]

I know that I can make an algorithm that will push these numbers and and operators onto a stack and pop them off and evaluate as I go. But, is there a better way to do with without using a external library?

Answer 1

Pushing the numbers and operators onto a stack would be an interpreter.

The obvious better way to do this (for some definition of "better") is to write a compiler!

You already have the input split into lexical tokens, so you can skip implementing a lexer and can dive right into building the AST. You can find suitable classes to transform your input to in the System.​Linq.​Expressions Namespace; have a look at the Expression Class. You can wrap the result in a lambda expression, compile it to IL and execute it on the CLR!

Answer 2

You can join the List and then let the compiler evaluate it at runtime as Mehrdad stated.

Expression e = new Expression("5 * 2"); 
e.Evaluate();

I found a very similar question already asked here

update :

NCalc "NCalc - Mathematical Expressions Evaluator for .NET" even though this is an external library I think it is an open source project which means you can add the code directly to your project.

Update :

You can use the String.Join function to join the List.

string formula = String.Join("",listMathOperators);

Answer 3

You can always use the C# compiler classes in the .NET framework to evaluate it as a C# expression...

Answer 4

I have a complete class that calculates any expression.

First, you need to extract all strings of your list to a single string, like:

string sExpression = "123+(890-15.00)";

Second, you need to evaluate this expression in a parser, I have a complete class that makes this for you, but I can't attach files here.