/in/foo.cc: In function 'int main()':
/in/foo.cc:6:2: error: 'cin' was not declared in this scope
  cin>>n;
  ^~~
/in/foo.cc:15:5: error: 'cout' was not declared in this scope
     cout<<sum<<"\n";
     ^~~~
/in/foo.cc:5:12: warning: unused variable 'x' [-Wunused-variable]
  int i,j,n,x,t=0,sum=0;
            ^