Adding until and unless to C

I have been looking into Ruby recently and find its keywords "until" and "unless" very interesting. So I thought what was a good way to add similar keywords into C/C++. Initially I attempted writing functions and then it struck me that this can be done with a simple macro. This is what I came up with:

#define until(x)    while(!(x))
#define unless(x)   if(!(x))

To illustrate my point here is a short factorial program:

I know that hacks like this do more harm than good in a large code base involving many programmers. But sometimes for small programs this can improve understandability dramatically.