Why an error when ORing switch case values?

Question

 switch (ch)
    {
    case '~' || 177: 
        tile->tileType = TILE_NONE;
        return true;
    case '@' || 219: //error here: '@'
        tile->tileType = TILE_WALL;
        return true; 
    }

The error reads: "case value '1' already used"

.....what the hell??

I've tried to clean the solution, restarted, used another PC. I'm "this close" to just reinstalling VS. Any idea what is happening?

C is a fairly simple and literal language. If you read up on what the `||` operator does, then it should shed light on the situation. — lurker, Dec 21 '19 at 00:52
How do you think reinstalling VS would fix an error in your code? Trust the compiler. When it says your code is wrong, it is certainly wrong. — abelenky, Dec 21 '19 at 02:29
@abelenky reinstalling VS is out of bounds, but restarting the PC isn't? The computer has trained Xolin_ well, lowering expectations about as far as they can go. — mevets, Dec 21 '19 at 03:28
The next question you will ask why is your char never 219... — Antti Haapala -- Слава Україні, Dec 21 '19 at 06:02

GBlodgett · Accepted Answer · 2019-12-21T16:18:28.427

You cannot have more than one case divided by || like you would an if statement. You have the case

'~' || 177:

Which is a boolean expression that evaluates to true, which gets evaluated to 1 because cases can only be an integral type (int, char and enum), so it must be converted to an int. So you are really saying

case 1:

The same thing happens in your second case statement, which is evaluated to a second case 1:, hence the error

Instead do:

case '~':
case 117:
   //code

score 2 · Answer 2 · answered Dec 21 '19 at 00:25

Instead of using a logical OR expression use the switch fall-through behavior:

switch (ch)
{
   case '~':
   case 117:
      tile->tileType = TILE_NONE;
      return true;
   case '@':
   case 219:
      tile->tileType = TILE_WALL;
      return true;
}

score 1 · Answer 3 · answered Dec 21 '19 at 00:03

'~' || 177 evaluates to true, which is 1.
So the line case '~' || 177: is really case 1:

Same with '@' || 219 in the line case '@' || 219:

You cannot have

switch (ch)
{
case 1: 
    tile->tileType = TILE_NONE;
    return true;
case 1: //  "case value '1' already used"  (You used it just above!)
    tile->tileType = TILE_WALL;
    return true; 
}

The error message is perfect and precise.
Why did you think you should reboot your PC or reinstall the IDE tools?

score 0 · Answer 4 · answered Dec 22 '19 at 19:50

the || operator just checks if any o the expressions at the sides is different from 0, and generates a true value of 1 if any of them is different from 0, so the first case is:

switch(...) {
case 1:

and the second case is also:

case 1:

so, the compiler cannot decide which case to follow.

Probably what you mean (and want to do) is this other thing:

switch (ch)
    {
    case '~': case 177: /* ch is either '~' or 177 */
        tile->tileType = TILE_NONE;
        return true;
    case '@': case 219: /* ch is either '@' or 219 */
        tile->tileType = TILE_WALL;
        return true; 
    }

which means that in case ch is any of '~' or 177, do the first part, and when it is '@' or 219, then go to the second part of the above code.

Why an error when ORing switch case values?

4 Answers4