Compilare: user.cpp: In function ‘void reverse_it()’: user.cpp:23:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < ans.size(); i++) ^ user.cpp: In function ‘int main()’: user.cpp:69:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < ans.size(); i++) ^ user.cpp:45:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("grafc.in","r",stdin); ^ user.cpp:46:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("grafc.out","w",stdout); ^ user.cpp:48:32: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d%d", &n, &a, &b); ^