Evaluator.cs

using System;
using System.Collections.Generic;

namespace Calculator
{
	public class Evaluator
	{
		readonly Queue<Token> postfixExpression;

		public Evaluator (Queue<Token> postfixExpression)
		{
			this.postfixExpression = postfixExpression;
		}

		public double Evaluate()
		{
			Stack<Token> evaluationStack = new Stack<Token> ();
			foreach (var token in postfixExpression) {
				if (token.Type == TokenType.Number) {
					evaluationStack.Push (token);
				} else if (token.Type == TokenType.Operator) {
					double result;
					Token temp = evaluationStack.Pop ();
					Operator op = new Operator (token);
					if (op.Op.Value == "#" || op.Op.Value == "@") {
						result = op.Operation (double.Parse (temp.Value));
					} else {
						string val1 = evaluationStack.Peek ().Value;
						result = op.Operation (Double.Parse (evaluationStack.Pop ().Value), Double.Parse (temp.Value));
					}
					evaluationStack.Push (new Token (result.ToString ()));
				} else if (token.Type == TokenType.Function) {
					double result = Function.Call (token.Value, evaluationStack);
					evaluationStack.Push (new Token (result.ToString ()));
				}
			}

			return Double.Parse (evaluationStack.Pop ().Value);
		}
	}
}