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?

>>103
How come you don't seem to have any issues understading the concept of the C abstract machine? Just curious because the other person who is calling me a a loser can't seem to grasp what is going on.