Compilare: user.cpp: In function ‘int main()’: user.cpp:19:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (D.size() >= l && nums[i] >= nums[D.front()]) { ^ user.cpp:32:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (D.size() >= l && D.size() <= u && sum > sol) ^ user.cpp:32:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (D.size() >= l && D.size() <= u && sum > sol) ^ user.cpp:12:32: 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:13:34: 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:15:31: 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:18:24: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &nums[i]); ^