Compilare: user.cpp: In function ‘bool sub(std::string, std::string)’: user.cpp:28:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i<x.size()&&j<y.size()) ^ user.cpp:28:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i<x.size()&&j<y.size()) ^ user.cpp:30:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(y[j]!=x[i]&&j<y.size()) j++; ^ user.cpp:33:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i==x.size()) return 1; ^ user.cpp: In function ‘int main()’: user.cpp:47:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(s.size()>mx) ^ user.cpp:52:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(s.size()==mx&&s<rz) rz=s; ^