Compilare: main.cpp: In function 'int main()': main.cpp:84:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<xx.size();i+=2){ ~^~~~~~~~~~ main.cpp:46:35: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("ratway.in", "r", stdin); ^ main.cpp:47:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ("ratway.out", "w", stdout); ^