Compilare: user.cpp: In function ‘bool check(int)’: user.cpp:82:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] return selected.size() <= k; ^ user.cpp: In function ‘int main()’: user.cpp:106:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 1; i <= n && selected.size() != k; i++) ^ user.cpp:87:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("salvare.in","r",stdin); ^ user.cpp:88:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("salvare.out","w",stdout); ^ user.cpp:91:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &n, &k); ^ user.cpp:93:30: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &x, &y); ^