Any variable has some space in the memory. A pointer references that space. The space that local variables occupies is deallocated when the function call returns, meaning that it can and will be reused for other things. As a consequence, references to that space are going to wind up pointing to something completely unrelated. Arrays in C are implemented as pointers, so this winds up applying to them. And constant arrays declared in a function also count as being local.
If you want to use an array or other pointer beyond the scope of the function in which it is created, you need to use malloc to reserve the space for it. Space reserved using malloc will not be reallocated or reused until it is explicitly released by calling free.
