Is there any difference in C and C++ between using if, else if, else if, ... and using switch () { case A: ... case B: ... }?

Question

I am interested if there is any difference from the C or C++ compiler perspective whether I use:

if (value == a) {
    ...
}
else if (value == b) { 
    ...
}
else if (value == c) { 
    ...
}

versus

switch (value) {
    case a:
        ...
        break;
    case b:
        ...
        break;
    case c:
        ...
        break;
}

It feels to me that there is no difference, just syntactic. Does anyone know more about it?

Thanks, Boda Cydo.

Answer 1

Yes, there are differences. The cascaded ifs guarantee evaluation of the conditions in order. The switch guarantees only a single evaluation of whatever's used as the switch parameter. Depending on the compiler, the switch will often take (nearly) constant time regardless of the selected branch, whereas the if cascade pretty much guarantees that the first leg is the fastest, the second second fastest, and so on down to the last being slowest.