Compilare: user.cpp: In function ‘void df(int)’: user.cpp:2:157: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] std::ifstream f("sortaret.in");std::ofstream o("sortaret.out");std::vector <int>a[50100];int i,j,x,y,n,m,d[50200];void df(int x){d[x]=1;for(j=0;i<a[x].size();j++)if(d[a[x][j]]==0)df(a[x][j]);o<<x<<" ";}main(){f>>n>>m;for(i=1;i<=m;i++)f>>x>>y,a[y].push_back(x);for(i=1;i<=n;i++)if(d[i]==0)df(i);} ^ user.cpp: At global scope: user.cpp:2:208: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type] std::ifstream f("sortaret.in");std::ofstream o("sortaret.out");std::vector <int>a[50100];int i,j,x,y,n,m,d[50200];void df(int x){d[x]=1;for(j=0;i<a[x].size();j++)if(d[a[x][j]]==0)df(a[x][j]);o<<x<<" ";}main(){f>>n>>m;for(i=1;i<=m;i++)f>>x>>y,a[y].push_back(x);for(i=1;i<=n;i++)if(d[i]==0)df(i);} ^