In a for loop, you need to separate the statements with semicolons, not commas.

You're not alone, I kept on doing that for a while too

By the way, you used "++w", shouldn't it be "w++"? I've seen both being used but I can't understand the different.

very different.  they both increment, but ++w applies before the value is taken into account, w++ applies after the whole line has been run through.

Just as a side note, it is more efficient to do ++w.  So if you don't need the value of w before it's incremented, then use ++w instead.

Except any good compiler will compile "w++" to the same as "++w" if the result isn't used. (I know the discussion ephan linked says that this might not be the case sometimes, but that's for C++) If precedent helps, I've always seen it written postfix for the loop increment.