Compilare: user.cpp: In function ‘int main()’: user.cpp:36:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ( IN , "r" , stdin ) ; ^ user.cpp:37:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen ( OUT , "w" , stdout ) ; ^ user.cpp:38:35: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf ( "%d %d\n" , &n , &m ) ; ^ user.cpp:44:43: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] for ( j = 0 ; j < m ; ++ j ) ^