Question

In C it’s possible to write code before the first case label. Are there any cases for which it is useful to do this or is it just a ‘dead block of code’ ?

E.g.:

switch (...)    {
  {
    int a = 0x2a;
    printf("%d\n", a);
  }
  case 0:
    ...
}

Answer 1

It can be useful to declare variables that have a scope limited to the switch block (but be aware that any initialisers for those variables will be skipped):

switch (...)
{
    int n;

    case 0:
    ...
}

In theory, you could also put code there that you get to using goto.