c - Pointer array assignments change pointer value directly -

there's multiple things might not potentially understand situation. i'm making own version of malloc, provided sbrk function gives me address use allocate memory on. address goes

void* heap = my_sbrk(stuff); 

i need put acquired space can give out in array. since heap pointer points start of available space do

freelist[7] = heap; 

now can implement function , works until does

freelist[7] = null; 

which results in heap becoming null

more if want change pointer pointing beginning address of heap, point null instead, heap ends pointing @ null.

is problem memory allocation? problem me misunderstanding how pointers work?

edit: nothing 'duplicate question', poster wants understand how memory allocated. want understand why changing value of element of pointer array changes object element pointing to.

namely, if

int* array; int value = 8; int* pointer = &value; array[0] = pointer; array[0] = null; 

i expect array[0] = null , *pointer = 8;