/in/foo.c:4:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:4:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c: In function 'main':
/in/foo.c:9:2: error: 'cin' undeclared (first use in this function)
  cin>>n;
  ^~~
/in/foo.c:9:2: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:14:4: error: 'cout' undeclared (first use in this function)
    cout<<" "<<setw(4)<<j*n+i;
    ^~~~
/in/foo.c:14:15: warning: implicit declaration of function 'setw' [-Wimplicit-function-declaration]
    cout<<" "<<setw(4)<<j*n+i;
               ^~~~
/in/foo.c:16:9: error: 'endl' undeclared (first use in this function)
   cout<<endl;
         ^~~~