Program won't crash when it should

(GCC C)
I ran a pointer over each member of an integer array, storing one character of input in each cell.

The program seems to consistently crash when I try to store X+3 or more characters, where X is the size of the array, but if I do not exceed X+2 it will not crash.

Why does it crashes exactly at the point it does, but not for X+1 or X+2?

>>52
The standard says that you're allowed to do int main(void) as well.

>>54
That happens at exit for any conforming implementation.

As I'm sure you know the return 0 in main is equivalent to calling exit with 0 as an argument which will flush all open streams with unwritten buffered data then close all open streams.

That's conforming to ISO/IEC 9899:2011 though, C89 behavior might be different I'm not certain what the guarantees are.