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?

>>18

Exactly. Thank you for your kind and precise observation, even if it was directed to a troll.

And yes, the behavior can change if different compiler settings are used.

To illustrate that using GCC, just compile the program with -O3 and you'll see that the control flow analysis has decided that f() does nothing, thus removing the call to it. The result is simply an empty program.