Evaluating string “3*(4+2)” yield int 18 [duplicate]

Answer 1

This is a simple Expression Evaluator using Stacks

public class MathEvaluator
{
    public static void Run()
    {
        Eval("(1+2)");
        Eval("5*4/2");
        Eval("((3+5)-6)");
    }

    public static void Eval(string input)
    {
        var ans = Evaluate(input);
        Console.WriteLine(input + " = " + ans);
    }

    public static double Evaluate(String input)
    {
        String expr = "(" + input + ")";
        Stack<String> ops = new Stack<String>();
        Stack<Double> vals = new Stack<Double>();

        for (int i = 0; i < expr.Length; i++)
        {
            String s = expr.Substring(i, 1);
            if (s.Equals("(")){}
            else if (s.Equals("+")) ops.Push(s);
            else if (s.Equals("-")) ops.Push(s);
            else if (s.Equals("*")) ops.Push(s);
            else if (s.Equals("/")) ops.Push(s);
            else if (s.Equals("sqrt")) ops.Push(s);
            else if (s.Equals(")"))
            {
                int count = ops.Count;
                while (count > 0)
                {
                    String op = ops.Pop();
                    double v = vals.Pop();
                    if (op.Equals("+")) v = vals.Pop() + v;
                    else if (op.Equals("-")) v = vals.Pop() - v;
                    else if (op.Equals("*")) v = vals.Pop()*v;
                    else if (op.Equals("/")) v = vals.Pop()/v;
                    else if (op.Equals("sqrt")) v = Math.Sqrt(v);
                    vals.Push(v);

                    count--;
                }
            }
            else vals.Push(Double.Parse(s));
        }
        return vals.Pop();
    }
}

Answer 2

I recently needed to do this for a project and I ended up using IronPython to do it. You can declare an instance of the engine, and then pass any valid python expression and get the result. If you're just doing simple math expressions, then it would suffice. My code ended up looking similar to:

IronPython.Hosting.PythonEngine pythonEngine = new IronPython.Hosting.PythonEngine();
string expression = "3*(2+4)";
double result = pythonEngine.EvaluateAs<double>(expression);

You'd probably not want to create the engine for each expression. You also need a reference to IronPython.dll