Whats the best way to conditionally control the direction of a for loop

Question

I've got a block in my code in which the for loop should run forwards or backwards depending on a condition.

if (forwards) {
    for (unsigned x = 0; x < something.size(); x++ ) {
        // Lots of code
    }

} else {
    for (unsigned x = something.size()-1 ; x >= 0 ; x-- ) {
        // Lots of code
    }
} 

Is there a nice way to set this up, so I don't repeat all the code within the for loop twice?

The 'something' in question is a std::vector<>, so maybe its possible with an iterator? (I'm not using C++11 )

Answer 1

Or you can do something like this:

for (unsigned x = (forward ? 0: something.size()); x != (forward ? something.size() :0); forward? x++: x-- ) {
    // Lots of code
}

The compiler will most likely optimize it and evaluate forward only once since it's value doesn't change in the for loop I assume.