Compilare: user.cpp: In function ‘int main()’: user.cpp:86:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0,ans=1;i<exp.size();++i) ^ user.cpp:78:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("multiplu2.in","r",stdin); ^ user.cpp:79:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("multiplu2.out","w",stdout); ^ user.cpp:81:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&N,&K); ^