Switch statement error

Questions & Answers
1

Hey guys,

I just “discovered” the switch statement today, and have been trying to figure it out. For some reason, the example I made is not working, and I would like to know why. If anyone can see what’s wrong, please post an answer! The code, as well as the error, are bellow.

error CS0152: The label `case -2:' already occurs in this switch statement

		switch(DateTime.Today.Month)
	{
	
	case 1:
		Debug.Log ("case 1");
		season = 3;
		world.renderer.material = winterGround;
		break;
	case 2 - 4:
		Debug.Log ("case 2 - 4");
		season = 0;
		world.renderer.material = springGround;
		break;
	case 5 - 7:
		Debug.Log ("case 5 - 7");
		season = 1;
		world.renderer.material = summerGround;
		break;
	case 8 - 10:
		Debug.Log ("case 8 - 10");
		season = 2;
		world.renderer.material = autumnGround;
		break;
	case 11 - 12:
		Debug.Log ("case 11 - 12");
		season = 3;
		world.renderer.material = winterGround;
		break;
	default:
		Debug.Log ("There is an error!");
		break;
	}

Thanks for your help!

-Gibson

2

“case 2 - 4:” is read as “case 2 minus 4”, which translates to -2. same for 5 - 7, etc.
A case can only contain one value. But you can do the following:

switch(DateTime.Today.Month)
{

case 1:
   Debug.Log ("case 1");
   season = 3;
   world.renderer.material = winterGround;
   break;
case 2:
case 3:
case 4:
   Debug.Log ("case 2 - 4");
   season = 0;
   world.renderer.material = springGround;
   break;
case 5:
case 6:
case 7:
...
break;
...
}

If you then call case 2 it will go through all the code until the next break statement. So case 2, case 3, and case 4 will all execute the same code.

3

Switches are very handy, but I think you might be misunderstanding one crucial detail: switches will only check for equality against individual constant values, not ranges or variables.

You set a number of cases using literal expressions:

case 2 - 4:
case 5 - 7:
case 8 - 10:

I’ve never seen that done, before, but I believe the compiler is simplifying all of those expressions. And what do they have in common? All of the expressions I quoted will evaluate to the same number:

case -2:
case -2:
case -2:
case -2:

Recognize that number from your error message?

Within a switch, each case value must be unique.

You may have an easier time with other control structures (array indexing, binary searching, a simple series of if-else blocks, or so on), but that seems to be beyond the scope of your original question.