Compilare: user.cpp: In function ‘long long unsigned int check(long long unsigned int)’: user.cpp:15:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1 ; i <= n ; ++ i) ^ user.cpp: In function ‘int main()’: user.cpp:43:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1 ; i <= n ; ++ i) { ^ user.cpp:50:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1 ; i <= n ; ++ i) { ^