Using the switch statement instead of if

Question

so I just started programming and I started with c#. In the book I'm reading (learning c# 3.0), one of the exercises was this.

Exercise 5-2. Create a program that prompts a user for input, accepts an integer, then evaluates whether that input is zero, odd or even, a multiple of 10, or too large (more than 100) by using multiple levels of if statements.

I managed to to this but the next exercise was

Exercise 5-3. Rewrite the program from Exercise 5-2 to do the same work with a switch statement.

I understand how switch statements work, but, I'm not sure how to work out if the user input number is odd/even, multiple of 10 and so on, and not use an if statement. Thank you for any help.

A switch with a boolean thing swithced on, and a case true and case false. — Benjamin Gruenbaum
– Benjamin Gruenbaum, Commented Aug 18, 2013 at 11:04
I can understand your problem. It seems like a bad exercise. It doesn't seem to be suited for a switch statement. Of course @BenjaminGruenbaum is right any if (b) { ... } else { ... } can be rewritten into switch (b) { case true: ...; break; default: ...; break; } but that is not a realistic use. You could take "odd or even" and "multiple of 10" together, assuming you made sure the number was not negative, by switching on num % 10, but I don't think that is a realistic use either. — Jeppe Stig Nielsen
– Jeppe Stig Nielsen, Commented Aug 18, 2013 at 11:17

p.s.w.g · Accepted Answer · 2013-08-18 11:40:18Z

1

You can do this:

int input = ...
switch (input)
{
    case 0:
        Console.WriteLine("Zero");
        default;
    default:
        switch (input < 100)
        {
            case true:
                switch (Math.Abs(input) % 10)
                {
                    case 0:
                        Console.WriteLine("Multiple of 10");
                        break;
                    case 2:
                    case 4:
                    case 6:
                    case 8:
                        Console.WriteLine("Even");
                        break;
                    default:
                        Console.WriteLine("Odd");
                        break;
                }
                break;
            default:
                Console.WriteLine("Too large");
                break;
        }
        break;
}

I don't think you can do this with a single switch in C#—unless you make it so massive as to account from every number from 0-100. You might be able to do it with a single Select statement in VB.NET, which is similar to a C# switch but has significantly different semantics.

edited Aug 18, 2013 at 11:40

answered Aug 18, 2013 at 11:08

p.s.w.g

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6 Comments

Sergey Berezovskiy Over a year ago

That should be never used in production code, but nice job :)

BitParser Over a year ago

What about input==0 ? Also try to respect the order in which the conditions were given

p.s.w.g Over a year ago

@TGO Thanks, I'd forgotten about the zero case. Although I don't think you can handle the conditions exactly in the order they were given. You have to check < 100 before you check whether it is divisible by 10 or 2.

BitParser Over a year ago

@p.s.w.g whatever, as Jeppe Stig Nielsen commented in the question, the exercise itself is ill formed

p.s.w.g Over a year ago

@TGO Agreed. This is not at all the kind of code I'd write in any real-world situation. There are much more relevant cases where a switch can be legitimately applied.

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