Using enums and checking if the user input is valid. I also added a loop that checks if the user wants to input equations.
References:
You can try it here: https://dotnetfiddle.net/aIwX5P
using System;
public class Program
{
enum eOperator
{
opAdd = 0,
opSub = 1,
opDiv = 2,
opMul = 3,
opInvalid = int.MinValue + 1,
opQuit = int.MinValue
}
public static void Main()
{
double a = 0.0, b = 0.0;
eOperator op = eOperator.opQuit;
string input = String.Empty;
Console.WriteLine("Calculator");
Console.WriteLine("Enter 'quit' at any time to exit.");
// repeat until the user wants to quit.
do // while(op != eOperator.opQuit)
{
Console.Write("a = ");
input = Console.ReadLine().ToLower().Trim();
if (double.TryParse(input, out a))
{
// input is a valid double and was stored in a
Console.Write("Operator: ");
input = Console.ReadLine().ToLower().Trim();
switch (input)
{
case "+":
op = eOperator.opAdd;
break;
case "-":
op = eOperator.opSub;
break;
case "*":
op = eOperator.opMul;
break;
case "/":
op = eOperator.opDiv;
break;
case "quit":
op = eOperator.opQuit;
break;
default:
op = eOperator.opInvalid; // can't be left as quit
Console.WriteLine("Invalid entry. +, -, *, / or quit for operator.");
break;
}
if (op != eOperator.opQuit && op != eOperator.opInvalid)
{
// user didn't choose to quit or type something invalid
Console.Write("b = ");
input = Console.ReadLine().ToLower().Trim();
if (double.TryParse(input, out b))
{
// input is a valid double and was parsed into b
double result = a; // we use the operator on a, so we might as well just store a into the result right away.
// do the operation on result.
switch (op)
{
case eOperator.opAdd:
result += b;
break;
case eOperator.opSub:
result -= b;
break;
case eOperator.opMul:
result *= b;
break;
case eOperator.opDiv:
// Div by 0 check. without this, this still works since double has +/- inf values.
if (b != 0.0) // comparing double with = and != is usually bad idea, but 0.0 is saved without rounding errors.
{
result /= b;
}
else
{
Console.WriteLine("Div by 0");
op = eOperator.opInvalid;
}
break;
default:
// this if branch checked for the other two operators. since we never chanced op after that check, this exception should never happen.
// it is still a good idea to include it to find errors in your logic, should they have occurred.
throw new Exception("This shouldn't happen.");
}
if (op != eOperator.opInvalid)
{
Console.WriteLine("Result: " + result.ToString());
}
// the only invalid operation is div by 0 for now. the message was sent to the user in that case, so no else is needed at this point.
// alternatively you can store an error message into a string, and when op = opInvalid, then display that error message here centralized.
// this would be a good idea if multiple things can go wrong.
}
else if (input == "quit")
{
// input for b was an invalid number, but input was 'quit'
op = eOperator.opQuit;
}
else
{
// input for b was an invalid number and also not 'quit', display error message
Console.WriteLine("Invalid entry. Type a number or Quit");
}
}
}
else if (input == "quit")
{
// input for a was invalid number, but 'quit'
op = eOperator.opQuit;
}
else
{
// input for a was invalid number and also not 'quit'
Console.WriteLine("Invalid entry. Type a number or Quit");
}
// repeat until the user wants to quit.
}while(op != eOperator.opQuit);
Console.WriteLine("Bye");
}
}
