Compilare: user.cpp: In function ‘int check(int)’: user.cpp:16:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(pos < a[i].first.size() && pos < a[i+1].first.size() && a[i].first[pos] == a[i+1].first[pos]) pos++; ^ user.cpp:16:59: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(pos < a[i].first.size() && pos < a[i+1].first.size() && a[i].first[pos] == a[i+1].first[pos]) pos++; ^