/in/foo.cc: In function 'int main()':
/in/foo.cc:2:5: error: 'string' was not declared in this scope
     string a;
     ^~~~~~
/in/foo.cc:3:5: error: 'cin' was not declared in this scope
     cin>>a;
     ^~~
/in/foo.cc:3:10: error: 'a' was not declared in this scope
     cin>>a;
          ^
/in/foo.cc:5:9: error: 'cout' was not declared in this scope
         cout<<a[i];
         ^~~~