Compilare: user.cpp: In function ‘int main()’: user.cpp:39:9: warning: unused variable ‘j’ [-Wunused-variable] int i, j, a, b; ^ user.cpp:37:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("reinvent.in", "rt", stdin); ^ user.cpp:38:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("reinvent.out", "wt", stdout); ^ user.cpp:40:34: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ("%d %d %d\n", &N, &M, &X); ^ user.cpp:44:27: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(sir, 256, stdin); ^ user.cpp:56:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d ", &a), ok[a] = 1; ^