c - What if I don't write default in switch case?

Question

int a = 10;
switch(a){
case 0:
    printf("case 0");
    break;
case 1:
    printf("case 1");
    break;
}

Is the above code valid?

If I am sure that int a will not have any other value than 1 and 0, can I avoid default?

What if in any case a value will be different from 1 and 0?

I know this is a silly question but I was thinking that perhaps it would be illegal or undefined behavior soI just asked to make sure.

Answer 1

The code is valid. If there is no default: label and none of the case labels match the "switched" value, then none of the controlled compound statement will be executed. Execution will continue from the end of the switch statement.

ISO/IEC 9899:1999, section 6.8.4.2:

[...] If no converted case constant expression matches and there is no default label, no part of the switch body is executed.