/in/foo.cc:2:1: error: 'uisng' does not name a type
 uisng namespace std;
 ^~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:6:1: error: 'cin' was not declared in this scope
 cin>>a>>b;
 ^~~
/in/foo.cc:6:1: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/6/iostream:60:18: note:   'std::cin'
   extern istream cin;  /// Linked to standard input
                  ^~~
/in/foo.cc:7:1: error: 'cout' was not declared in this scope
 cout<<a+b<<endl;
 ^~~~
/in/foo.cc:7:1: note: suggested alternative:
In file included from /in/foo.cc:1:0:
/usr/include/c++/6/iostream:61:18: note:   'std::cout'
   extern ostream cout;  /// Linked to standard output
                  ^~~~
/in/foo.cc:7:12: error: 'endl' was not declared in this scope
 cout<<a+b<<endl;
            ^~~~
/in/foo.cc:7:12: note: suggested alternative:
In file included from /usr/include/c++/6/iostream:39:0,
                 from /in/foo.cc:1:
/usr/include/c++/6/ostream:590:5: note:   'std::endl'
     endl(basic_ostream<_CharT, _Traits>& __os)
     ^~~~