Dangling and NULL Pointers

int *p = NULL;
if (p != NULL) *p = 5;            // always check before dereferencing

int *make(void) {
    int local = 5;
    return &local;                // BUG: dangling — local dies when the function returns
}

free(buf);
buf = NULL;                       // avoid a dangling pointer after free

Dereferencing NULL usually crashes; dereferencing a dangling pointer silently corrupts data — much harder to debug. Tools like AddressSanitizer and Valgrind find these bugs.