C# SimpleCalculator

Question

I am trying to write a code for a SIMPLE Calculator and I am getting some errors:

following is the errors:

Error 1 The name 'Valid' does not exist in the current context
Error 2 The name 'Subtract'/add/multiply, divide does not exist in the current context

Please see what is wring with the code and suggest what i am doing wrong.

 int input = 0;
 double num1 = 0;
 double num2 = 0;
 string inputN1 = "";
 string inputN2 = "";
 bool validnum1 = true;
 bool validnum2 = true;

 do{
     Console.WriteLine("Simple Calculator\n\t 1) Add\n\t 2) Subtract\n\t 3) 
     Multiply\n\t 4) Divide\n\t 5) Quit\n\t ", input);
     Console.Write("Enter your Selection: ");
     input = Convert.ToInt32(Console.ReadLine());

     if (input ==5)
     {
        Console.WriteLine();
     }
     else if (input >5)
     {
        Console.WriteLine("Invalid Selection.\t Please Try Again");
     }
     else
     {
        Console.Write("Enter Number 1: ");
        inputN1 = Console.ReadLine();
        validnum1 = Valid(inputN1);
        Console.Write("Enter Number 2: ");
        validnum2 = Valid(inputN2);

        if (validnum1 == true && validnum2 == true)
        {
              num1 = Convert.ToDouble(inputN1);
              num2 = Convert.ToDouble(inputN2);
        }
        else 
        {
             Console.WriteLine("Invalid Number Entered");
             Console.ReadKey();
             break;
         }

         switch (input)
         {
            case 1:
                   Console.WriteLine("\tResults: {0}", Add(num1, num2));
                   break;
            case 2:
                   Console.WriteLine("\tResults: {0}", Subtract(num1, num2));
                   break;
            case 3:
                   Console.WriteLine("\tResults: {0}", Multiply(num1, num2));
                   break;
            case 4:
                   if (num2 == 0)
                   {
                      Console.WriteLine("Cant Divide by Zero/\t Please try Again");
                   }
                   else
                   {
                      Console.WriteLine("\tResults: {0}", Divide(num1, num2));
                   }
                   break;
           }
           Console.WriteLine("Press any key...");
           Console.ReadKey();
           Console.Clear();
       }

   }while (input != 5 && input <5);

      Console.WriteLine("Press any key....");
      Console.ReadKey();

 }

            }
        }

Answer 1

First of All there is no such thing in C# as Valid, Subtract, Add and Multiply. To check whether a given string is valid double use double.TryParse(). For Arithmetic operations use +,-,*,/ for Add, Subtract, Multiply and Divide respectively. Instead try to use this code it will work. If you are using Methods then access them through Class specifier like this Your_Class.Add() because to access Non-Static Methods from Static class you need class instance containing the non-static method.

int input = 0;
        double num1 = 0;
        double num2 = 0;
        string inputN1 = "";
        string inputN2 = "";
        bool validnum1 = true;
        bool validnum2 = true;

        do{
            Console.WriteLine("Simple Calculator\n\t 1) Add\n\t 2) Subtract\n\t 3) Multiply\n\t 4) Divide\n\t 5) Quit\n\t ", input);
            Console.Write("Enter your Selection: ");
            input = Convert.ToInt32(Console.ReadLine());

            if (input ==5)
            {
                Console.WriteLine();
            }
            else if (input >5)
            {
                Console.WriteLine("Invalid Selection.\t Please Try Again");
            }

            else
            {
                Console.Write("Enter Number 1: ");
                inputN1 = Console.ReadLine();
                validnum1 = double.TryParse(inputN1,out num1);
                Console.Write("Enter Number 2: ");
                inputN2 = Console.ReadLine();
                validnum2 = double.TryParse(inputN2,out num2);

                if (validnum1 != true || validnum2 != true)
                {
                    Console.WriteLine("Invalid Number Entered");
                    Console.ReadKey();
                    break;
                   // num1 = Convert.ToDouble(inputN1);
                   // num2 = Convert.ToDouble(inputN2);
                }

                //else  else will not be required as double.tryparse is succeeded then value will automatically assigned to respective numbers.
                //{

                //}

                switch (input)
                {
                    case 1:
                        Console.WriteLine("\tResults: {0}", num1+num2);
                        break;
                    case 2:
                        Console.WriteLine("\tResults: {0}", num1-num2);
                        break;
                    case 3:
                        Console.WriteLine("\tResults: {0}", num1*num2);
                        break;
                    case 4:
                        if (num2 == 0)
                        {
                            Console.WriteLine("Cant Divide by Zero/\t Please try Again");
                        }
                        else
                        {
                            Console.WriteLine("\tResults: {0}", num1/num2);
                        }
                        break;
                }
                Console.WriteLine("Press any key...");
                Console.ReadKey();
                Console.Clear();
            }


        }while (input != 5 && input <5);

        Console.WriteLine("Press any key....");
        Console.ReadKey();

    }

    }
}