Compilare: user.cpp: In function ‘int Pairup(int)’: user.cpp:49:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < V[x].size(); ++ i) ^ user.cpp: In function ‘void read()’: user.cpp:61:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("plan.in", "r", stdin); ^ user.cpp:62:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &n, &m); ^ user.cpp:66:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &x, &y); ^ user.cpp: In function ‘void write()’: user.cpp:189:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("plan.out", "w", stdout); ^