Compilare: main.cpp: In function 'void back(int)': main.cpp:9:8: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] {if( l == k ){for(int i = 1; i<=k;++i)out<<v[i]<<" ";out<<'\n'; ~~^~~~ main.cpp:9:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] {if( l == k ){for(int i = 1; i<=k;++i)out<<v[i]<<" ";out<<'\n'; ~^~~ main.cpp:10:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] }else for(int i = v[l]+1 ; i<=n; ++i){v[l+1] = i;back(l+1);} ~^~~