Compilare: main.cpp: In function 'int main()': main.cpp:25:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1;i<s.size()-1;++i) { ~^~~~~~~~~~~ main.cpp:40:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<s.size();++i) { ~^~~~~~~~~ main.cpp:16:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("charlie.in","r",stdin); ^ main.cpp:17:38: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("charlie.out","w",stdout); ^