Compilare: user.c: In function ‘add’: user.c:30:13: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration] _node->next = malloc(sizeof(node)); ^ user.c:30:27: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default] _node->next = malloc(sizeof(node)); ^ user.c: In function ‘rem’: user.c:48:12: warning: unused variable ‘next’ [-Wunused-variable] node * next = _node->next; ^ user.c: In function ‘main’: user.c:88:18: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default] node *hash = malloc(sizeof(node) * HASH_KEY); ^