I found a site with some complicated C puzzles. Right now I'm dealing with this:

The following is a piece of C code, whose intention was to print a minus sign 20 times. But you can notice that, it doesn't work.

#include <stdio.h>
int main()
{
    int i;
    int n = 20;
    for( i = 0; i < n; i-- )
        printf("-");
    return 0;
}

Well fixing the above code is straight-forward. To make the problem interesting, you have to fix the above code, by changing exactly one character. There are three known solutions. See if you can get all those three.

I cannot figure out how to solve. I know that it can be fixed by changing -- to ++, but I can't figure out what single character to change to make it work.