The behavior of your program is undefined. The fact that it compiles at all is because of the cast, which effectively tells the compiler "this is wrong, but do it anyway". If you remove the cast, you'll get the appropriate error message:
a.c:17:8: error: assignment from incompatible pointer type [-Werror]
(From gcc -Wall -Werror.)
More specifically, the behavior depends on the calling conventions. If you were on a platform were the arguments were passed in "reverse" order on the stack, the program would give a very different result.
