Puzzle (coding)

from XKCD wiki thingy

Find three ways to make the C program below print 20 copies of the dash character '-' by changing/adding one character:

Code:

int i, n = 20;
for (i = 0; i < n; i--)
{
    printf("-");
}

I've only found one, but I'm stupid

Spoilerplz.

Also:
* Find a way to get it to print exactly 21 dashes (changing 1 character).
* Find a way to get it to print exactly 1 dash (changing one character).
* Print 20 dashes with the given code, without changing it at all, but adding some preceding code.
* Print 1 dash with the given code, without changing it at all, but adding some preceding code.