Benefit of using short instead of int in for... loop

No, there is no benefit. The short will probably end up taking a full register (which is 32 bits, an int) anyway.

You will lose hours typing the extra two letters in the IDE, too. (That was a joke).

No. The loop variable will likely be allocated to a register, so it will end up taking up the same amount of space regardless.

Nope. Chances are your counter will end up in a register anyway, and they are typically at least the same size as int

As most others have said, computationally there is no advantage and might be worse. However, if the loop variable is used in a computation requiring a short, then it might be justified:

for(short j = 0; j < 5; j++)
{
   // void myfunc(short arg1);
   myfunc(j);
}

All this really does is prevent a warning message as the value passed would be promoted to an int (depending on compiler, platform, and C++ dialect). But it looks cleaner, IMHO.

Certainly not worth obsessing over. If you are looking to optimize, remember the rules (forget who came up with these):

1. Don't
2. Failing Step 1, first Measure
3. Make a change
4. If bored, exit, else go to Step 2.