C# how to use enum with switch

Question

I can't figure out how to use switches in combination with an enum. Could you please tell me what I'm doing wrong, and how to fix it? I have to use an enum to make a basic calculator.

public enum Operator
{
    PLUS, MINUS, MULTIPLY, DIVIDE
}

public double Calculate(int left, int right, Operator op)
{

    int i = (int) op;

    switch(i)
    {
        case 0:
        {
            return left + right;
        }

        case 1:
        {
            return left - right;
        }

        case 2:
        { 
            return left * right;
        }

        case 3:
        {
            return left / right;
        }

        default:
        {
            return 0.0;
        }
    }
}

The end result should be something like this:

Console.WriteLine("The sum of 5 and 5 is " + Calculate(5, 5, PLUS))
Output: The sum of 5 and 5 is 10

Could you guys please tell me how I'm messing up?

Answer 1

You don't need to convert it

switch(op)
{
     case Operator.PLUS:
     {
        // your code 
        // for plus operator
        break;
     }
     case Operator.MULTIPLY:
     {
        // your code 
        // for MULTIPLY operator
        break;
     }
     default: break;
}

By the way, use brackets

Answer 2

Since C# 8.0 introduced a new switch expression for enums you can do it even more elegant:

public double Calculate(int left, int right, Operator op) =>
            op switch 
        {
            Operator.PLUS => left + right,
            Operator.MINUS => left - right,
            Operator.MULTIPLY => left * right,
            Operator.DIVIDE => left / right,
            _    =>  0
        }

Ref. https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8

Answer 3

The correct answer is already given, nevertheless here is the better way (than switch):

private Dictionary<Operator, Func<int, int, double>> operators =
    new Dictionary<Operator, Func<int, int, double>>
    {
        { Operator.PLUS, ( a, b ) => a + b },
        { Operator.MINUS, ( a, b ) => a - b },
        { Operator.MULTIPLY, ( a, b ) => a * b },
        { Operator.DIVIDE ( a, b ) => (double)a / b },
    };

public double Calculate( int left, int right, Operator op )
{
    return operators.ContainsKey( op ) ? operators[ op ]( left, right ) : 0.0;
}