static void Main(string[] args) { Calculator c = new Calculator(); // Calculator c2 = new Calculator(); // Console.WriteLine(Math.Round(c2.Tan(20), 4)); double n1 = 0, n2; string again = ""; bool keep = true; do { do { keep = true; try { Console.WriteLine("This is a Calculator, enter number, action, number "); Console.WriteLine("Available Actions : "); Console.WriteLine("+ - * / % pow sqrt sine cos tan "); n1 = double.Parse(Console.ReadLine()); } catch (Exception ex) { Console.WriteLine(ex.Message); keep = false; } } while (keep == false); string action = (Console.ReadLine()); if ((action.ToUpper() != "SQRT") && (action.ToUpper() != "SINE") && (action.ToUpper() != "COS") && (action.ToUpper() != "TAN")) { n2 = int.Parse(Console.ReadLine()); } else { n2 = 0; } if (action == "+") { Console.WriteLine("Answer is " + c.Add(n1, n2)); } else if (action == "-") { Console.WriteLine(c.Sub(n1, n2)); } else if (action == "*") { Console.WriteLine(c.Mul(n1, n2)); } else if (action == "/") { Console.WriteLine(c.Div(n1, n2)); } else if (action == "%") { Console.WriteLine(c.Mod(n1, n2)); } else if (action.ToUpper() == "POW") { Console.WriteLine(c.Power(n1, n2)); } else if (action.ToUpper() == "SQRT") { Console.WriteLine(c.Sqrt(n1)); } else if (action.ToUpper() == "SINE") { Console.WriteLine(c.Sine(n1)); } else if (action.ToUpper() == "COS") { Console.WriteLine(c.Cos(n1)); } else if (action.ToUpper() == "TAN") { Console.WriteLine(c.Tan(n1)); } else { Console.WriteLine("Invalid Entry"); } Console.WriteLine("Continue, Yes or No? "); again = Console.ReadLine(); } while (again.ToUpper() == "YES"); }