Very simple C# console calculator with parsing

using System;


namespace Simple_Calculator
{

    class Program
    {
        class calculator
        {
            int numberOne = 0;
            int numberTwo = 0;
            int sum = 0;
            void loadNumbers(int one, int two)
            {
                numberOne = one;
                numberTwo = two;
            }

            public int parseAndCompute(string str)
            {
                string[] numbers;
                if (str.Contains("*")) {
                    numbers = str.Split("*");
                    numberOne = int.Parse(numbers[0]);
                    numberTwo = int.Parse(numbers[1]);
                    sum = numberOne * numberTwo;
                    return sum;
                } else if (str.Contains("+"))
                {
                    numbers = str.Split("+");
                    numberOne = int.Parse(numbers[0]);
                    numberTwo = int.Parse(numbers[1]);
                    sum = numberOne + numberTwo;
                    return sum;
                }
                else if (str.Contains("-"))
                {
                    numbers = str.Split("-");
                    numberOne = int.Parse(numbers[0]);
                    numberTwo = int.Parse(numbers[1]);
                    sum = numberOne - numberTwo;
                    return sum;
                } else if (str.Contains("/"))
                {
                    numbers = str.Split("/");
                    numberOne = int.Parse(numbers[0]);
                    numberTwo = int.Parse(numbers[1]);
                    sum = numberOne / numberTwo;
                    return sum;
                }
                else if (str.Contains("%")) // We could easily improve the program by allowing user to input "MODULUS" or "OR" or "AND" instead of %, |, %
                {
                    numbers = str.Split("%");
                    numberOne = int.Parse(numbers[0]);
                    numberTwo = int.Parse(numbers[1]);
                    sum = numberOne % numberTwo;
                    return sum;
                }
                else if (str.Contains("&"))
                {
                    numbers = str.Split("&");
                    numberOne = int.Parse(numbers[0]);
                    numberTwo = int.Parse(numbers[1]);
                    sum = numberOne & numberTwo;
                    return sum;
                }
                else if (str.Contains("|"))
                {
                    numbers = str.Split("|");
                    numberOne = int.Parse(numbers[0]);
                    numberTwo = int.Parse(numbers[1]);
                    sum = numberOne | numberTwo;
                    return sum;
                }
                return 0;
            }

        }
        static void Main(string[] args)
        {
            bool programRunning = true;
            while (programRunning)
            {
                Console.WriteLine("Type in ýour mathematical operation!");
                string oper = Console.ReadLine();
                calculator cCalc = new calculator();
                int answer = cCalc.parseAndCompute(oper);

                Console.WriteLine("The answer to: " + oper + " is: " + answer);
                Console.WriteLine("Do you wish to run another expression?(yes or no)");
                string cont = Console.ReadLine();
                if (cont.CompareTo("yes") == 0)
                    continue;
                else
                    programRunning = false;


            }
        }
    }
}