IF else in Switch Case

Question

int flag = 0;
char a = 'b';
switch(a) {
  case 'a':
    cout << "In a";
    break;
  if(flag!=0) {
    case 'b':
      cout << "In b";
      break;
  }
  case 'c':
    cout << "In c";
    break;
  default:
    cout << "In d";
}

Can someone explain why the above code is printing "In b"? As per my understanding, it should print "In d"

I have duplicated your result: [https://ideone.com/zIrqAk](https://ideone.com/zIrqAk) — drescherjm, Aug 16 '20 at 14:34
`case 'a': cout << "In a"; break; if(flag!=0) { case 'b': cout << "In b"; break; }` Will never reach your `if` because you already broke out of that `case` with the `break` statement just above it. — Jesper Juhl, Aug 16 '20 at 14:38
You can search for Duff's device, it uses the same principle — Steve Wilson, Aug 16 '20 at 14:41
[http://pigeonsnest.co.uk/stuff/pigeons-device.html](http://pigeonsnest.co.uk/stuff/pigeons-device.html) — drescherjm, Aug 16 '20 at 15:15
Here is a recursive solution that does what you want to do: https://godbolt.org/z/41o819 by combining `if` and `switch`. — User12547645, Aug 16 '20 at 17:10

Hi - I love SO · Answer 1 · 2020-08-16T14:46:30.957

2

Because a case 'a': is effectually a label to which the control flow is redirected at switch (a). In addition to not being able to modify compile-time structures, an if statement couldn't prevent this redirection simply because it is never reached in beforehand, as a result of aforementioned semantic.

edited Aug 16 '20 at 14:46

answered Aug 16 '20 at 14:36

Hi - I love SO

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If addition to mentioning "how", you could state the end result: you cannot enable/disable any case label by logic around it. – Jeffrey Aug 16 '20 at 14:38
Edited with an explanation. – Hi - I love SO Aug 16 '20 at 14:46

score 2 · Answer 2 · edited Aug 16 '20 at 14:51

2

the switch case mechanism is like goto call its jump to the relevant case if you will look at the assembly code here you will see that it translate to CMP and jmp or je command

edited Aug 16 '20 at 14:51

ChrisMM

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answered Aug 16 '20 at 14:42

yaodav

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IF else in Switch Case

2 Answers2