Difference between the address space of parent process and its child process in Linux?

I am confused about something. I have read that when a child is created by a parent process, the child gets a copy of its parent's address space. What does it mean by copy? If I use the code below, then it prints the same value for variable 'a' which is on the heap in both tthe child and parent. So what is happening here?

int main ()
{
        pid_t pid;
        int *a = (int *)malloc(4);
        printf ("heap pointer %p\n", a);
        pid = fork();
        if (pid < 0) {
                fprintf (stderr, "Fork Failed");
                exit(-1);
        }
        else if (pid == 0) {
                printf ("Child\n");
                printf ("in child heap pointer %p\n", a);
        }
        else {

                wait (NULL);
                printf ("Child Complete\n");
                printf ("in parent heap pointer %p\n", a);
                exit(0);
        }
}