/in/foo.c:2:1: error: unknown type name 'using'
 using namespace std;
 ^~~~~
/in/foo.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
 using namespace std;
                 ^~~
/in/foo.c: In function 'main':
/in/foo.c:4:2: error: 'intA' undeclared (first use in this function); did you mean 'int'?
  intA,B;
  ^~~~
  int
/in/foo.c:4:2: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:4:7: error: 'B' undeclared (first use in this function)
  intA,B;
       ^
/in/foo.c:4:6: warning: left-hand operand of comma expression has no effect [-Wunused-value]
  intA,B;
      ^
/in/foo.c:5:2: error: 'cin' undeclared (first use in this function); did you mean 'main'?
  cin>>A>>B;
  ^~~
  main
/in/foo.c:5:7: error: 'A' undeclared (first use in this function)
  cin>>A>>B;
       ^
/in/foo.c:6:5: error: 'cout' undeclared (first use in this function)
     cout<<A+B;
     ^~~~