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

Answer 1

This is right to left execution, so need to use proper parathesis to execute expression

    // 2+(100/5)+10 = 32
    //((2.5+10)/5)+2.5 = 5
    // (2.5+10)/5+2.5 = 1.6666
    public static double Evaluate(String expr)
    {

        Stack stack = new Stack();

        string value = "";
        for (int i = 0; i < expr.Length; i++)
        {
            String s = expr.Substring(i, 1);
            char chr = s.ToCharArray()[0];

            if (!char.IsDigit(chr) && chr != '.' && value != "")
            {
                stack.Push(value);
                value = "";
            }

            if (s.Equals("(")) {

                string innerExp = "";
                i++; //Fetch Next Character
                int bracketCount=0;
                for (; i < expr.Length; i++)
                {
                    s = expr.Substring(i, 1);

                    if (s.Equals("("))
                        bracketCount++;

                    if (s.Equals(")"))
                        if (bracketCount == 0)
                            break;
                        else
                            bracketCount--;


                    innerExp += s;
                }

                stack.Push(Evaluate(innerExp).ToString());

            }
            else if (s.Equals("+")) stack.Push(s);
            else if (s.Equals("-")) stack.Push(s);
            else if (s.Equals("*")) stack.Push(s);
            else if (s.Equals("/")) stack.Push(s);
            else if (s.Equals("sqrt")) stack.Push(s);
            else if (s.Equals(")"))
            {
            }
            else if (char.IsDigit(chr) || chr == '.')
            {
                value += s;

                if (value.Split('.').Length > 2)
                    throw new Exception("Invalid decimal.");

                if (i == (expr.Length - 1))
                    stack.Push(value);

            }
            else
                throw new Exception("Invalid character.");

        }


        double result = 0;
        while (stack.Count >= 3)
        {

            double right = Convert.ToDouble(stack.Pop());
            string op = stack.Pop();
            double left = Convert.ToDouble(stack.Pop());

            if (op == "+") result = left + right;
            else if (op == "+") result = left + right;
            else if (op == "-") result = left - right;
            else if (op == "*") result = left * right;
            else if (op == "/") result = left / right;

            stack.Push(result.ToString());
        }


        return Convert.ToDouble(stack.Pop());
    }