Compilare: user.cpp: In function ‘void use_a_square(int)’: user.cpp:36:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (valid.count() == n) return; ^ user.cpp: In function ‘bool check(int)’: user.cpp:78:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (valid.count() != n) return false; ^ user.cpp: In function ‘int main()’: user.cpp:84:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("patrate.in","r",stdin); ^ user.cpp:85:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("patrate.out","w",stdout); ^ user.cpp:87:19: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&n); ^ user.cpp: In member function ‘void Point::init()’: user.cpp:23:28: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&x,&y); ^