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?

Solution 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

Solution 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://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8

Solution 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;
}

Solution 4

You should not cast to integer. And for the division, you need to cast left to double first, if not you will be doing an integer divide.

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

public double Calculate(int left, int right, Operator op)
{
    double sum = 0.0;

    switch(op)
    {
       case Operator.PLUS:
       sum = left + right;
       return sum;

       case Operator.MINUS:
       sum = left - right;
       return sum;

       case Operator.MULTIPLY:
       sum = left * right;
       return sum;

       case Operator.DIVIDE:
       sum = (double)left / right;
       return sum;

       default:
       return sum;
   }

   return sum;
}

Solution 5

simply don't cast to int

 switch(operator)
    {
       case Operator.Plus:
       //todo

View more solutions

Comments

[Stephan Bauer]

Well .. yes, kind of... :-D

[Stephan Bauer]

@J.Starkl Well that's a matter of opinion, I think :-)

[J.Starkl]

@StephanBauer: Yes, it is :-)

[Kenneth K.]

More of an indent man, myself =) Strangely enough, that's the only thing I don't put braces on. Go figure!

[Matthew Watson]

If you ever introduce a new variable for use in a single case, you do of course need to use brackets. And at that point my OCD kicks in and I need to make all the cases look the same by adding brackets to them. (In all seriousness, I use brackets in switch statements because I use them for blocks everywhere else.)

[Chris Dunaway]

I think this is an example of where using var to declare the variable would be appropriate!

[JustAndrei]

Var cannot be used outside the method body.

[Chris Dunaway]

Oh yes, I missed that it was declared outside of the method.

[Stephan Bauer]

@MatthewWatson Great! Thanks for mentioning that point with variabloes for a single case - never thought of that :-)

[Adassko]

You can use using OperatorsDict = Dictionary<Operator, Func<int, int, double>> and then use OperatorsDict instead

[Rafe]

C# can have multi-line blocks without brackets since all must terminate with a return or break, goto or have no code at all. Fall-through is not allowed outside of these options: stackoverflow.com/questions/174155/…

[J.Starkl]

Yes, but if you use them everywhere -no pitfalls -consistent code -improved readability -simpler maintenence/extension -best practice (get used to them)

[Stix]

@JustAndrei - (I know it is an old post) Why is this method better than switch - is it faster ? or is it preference ? I would like to know not for arguments sake but better coding - I have always used switch but never thought to use a dictionary function. Certainly should not be in a serializable object.. of course Adassko's comment kind of makes my thoughts on a memory issue go away.

[JustAndrei]

1. Separation of configuration and logic: your code becomes short and easy to read. Your configuration reads like a table, what is easy as well. 2. Unlike switch, Dictionary internally uses a hashtable for fast lookup, what becomes significant when there are many cases. Sometimes programmers put the most used item at the end of the switch and have problems with performance. 3. Once the configuration is extracted from the code, now you can make a lot of great things:

[JustAndrei]

A. Move it from the code to an external source, e.g. configuration file or database. B. Dynamically modify configuration upon your needs, right while program execution. C. Create a plugin system, so that your configuration is extended by modules. D. Although Dictionary already helps to search the key faster, you can make it even better by customizing the way you lookup the operation. Once I implemented such a replacement for the switch, which accumulated case usage statistics during program execution, and periodically re-arranged the list of cases so that the most popular one became the first.

[BillW]

I'd like to see one reliable piece of evidence that Dictionary look-up is faster than 'Switch with Enums.

[IARI]

about the readability - I find python and haskell code way easier to read than c# or java

[Matthieu Charbonnier]

Note that the brackets isn't related to the switch/case: You can add brackets anywhere you want to separate variables.

[Nadav]

Switch case enables you to reuse the same code block for multiple cases. If you do - make sure to not use brackets.

[tekHedd]

I think it's a bit odd that you use braces for every case (so they'll match) but...not for "default:"...heck default is even on the same line, not matching the other cases. Not exactly criticizing, just enjoying how different people define "consistent" in different ways.

[tekHedd]

Unclear how this makes the code more readable, other than to enforce project-local style conventions. OP's example block of code is a classic example of how early-return can make code more readable.

[tekHedd]

This answer illustrates perfectly the right time to break the convention and use 1) early return from a function and 2) putting the case on the same line as the code.

[0b101010]

Any syntactic sugar which reduces the need for curly braces is good.

[0b101010]

@BillW You won't, because it isn't. Using a dictionary for this is a simply dreadful design choice.

[Mindaugas Bernatavičius]

Please cast one of the divided values into a double, don't confuse newcomers and spread incorrect code.