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?

>>32
What's unclear exactly?

He stated that you might look at the assembly output of a compiler to tell what a program as defined by the C code is doing, especially that you were able to do so in the face of undefined behavior in the C code so that undefined behavior might become "defined" by the implementation.

I said that isn't possible since the compiler might not produce the same assembly output every time.