Compilare: user.cpp: In function ‘int ok(int)’: user.cpp:27:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(value.size()<(1<<l)) ~~~~~~~~~~~~^~~~~~~ user.cpp:29:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<value.size();j++) ~^~~~~~~~~~~~~ user.cpp: In function ‘int main()’: user.cpp:44:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("string.in","r",stdin); ^ user.cpp:45:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("string.out","w",stdout); ^