Compilare: user.cpp: In function ‘int main()’: user.cpp:20:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (D.size() >= l && nums[D.front()] <= 0) { ^ user.cpp:28:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (D.size() > u) { ^ user.cpp:33:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (D.size() >= l && D.size() <= u && sum > sol) ^ user.cpp:33:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (D.size() >= l && D.size() <= u && sum > sol) ^ user.cpp:13:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sum2.in", "r", stdin); ^ user.cpp:14:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sum2.out", "w", stdout); ^ user.cpp:16:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d %d", &n, &l, &u); ^ user.cpp:19:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &nums[i]); ^