Compilare: user.c: In function ‘add’: user.c:13:5: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration] nod_t *p = malloc(sizeof(nod_t)); ^ user.c:13:16: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default] nod_t *p = malloc(sizeof(nod_t)); ^ user.c: In function ‘read’: user.c:25:11: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f, "%d %d", &n, &m); ^ user.c:28:15: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f, "%d %d", &x, &y); ^