Valid, but worthless syntax in switch-case?

Question

Through a little typo, I accidentally found this construct:

int main(void) {
    char foo = \'c\';

    switch(foo)
    {
        printf(\"Cant Touch This\\n\");         


        

Answer 1

It should be noted, that there are virtually no structural restrictions on the code within the switch statement, or on where the case *: labels are placed within this code*. This makes programming tricks like duff's device possible, one possible implementation of which looks like this:

int n = ...;
int iterations = n/8;
switch(n%8) {
    while(iterations--) {
        sum += *ptr++;
        case 7: sum += *ptr++;
        case 6: sum += *ptr++;
        case 5: sum += *ptr++;
        case 4: sum += *ptr++;
        case 3: sum += *ptr++;
        case 2: sum += *ptr++;
        case 1: sum += *ptr++;
        case 0: ;
    }
}

You see, the code between the switch(n%8) { and the case 7: label is definitely reachable...

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* _{As supercat thankfully pointed out in a comment: Since C99, neither a goto nor a label (be it a case *: label or not) may appear within the scope of a declaration that contains a VLA declaration. So it's not correct to say that there are no structural restrictions on the placement of the case *: labels. However, duff's device predates the C99 standard, and it does not depend on VLA's anyway. Nevertheless, I felt compelled to insert a "virtually" into my first sentence due to this.}