Compilare: user.cpp: In function ‘int cost(std::string)’: user.cpp:38:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0,p5=1;i<a.size();i++,p5*=5) ^ user.cpp: In function ‘int main()’: user.cpp:64:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("ninjago.in","r",stdin); ^ user.cpp:65:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("ninjago.out","w",stdout); ^