Compilare: user.cpp: In function ‘int main()’: user.cpp:37:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < s.size()) { ^ user.cpp:44:46: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < stck.size(); i++) { ^ user.cpp:30:31: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("dir.in", "r", stdin); ^ user.cpp:31:32: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("dir.out","w", stdout); ^