#include <stdio.h>

int main() {
  int mode = 0;
  int doipass = 1; // changed between tests
  for (mode = 0; mode < 3; mode++) {
    printf("We're in mode %i and the if will %sfail\n", mode, doipass?"not ":"");
    switch (mode) {
      case 0: if (doipass) {
      case 1:   printf("case1\n");
                break;
              } else {
      case 2:   printf("case2\n");
                break;
              }
    }
  }
}

ultimation@NoizeBox:~/temp$ ./test
We're in mode 0 and the if will fail
case2
We're in mode 1 and the if will fail
case1
We're in mode 2 and the if will fail
case2

ultimation@NoizeBox:~/temp$ ./test
We're in mode 0 and the if will not fail
case1
We're in mode 1 and the if will not fail
case1
We're in mode 2 and the if will not fail
case2