foo.c: In function 'main':
foo.c:6:2: error: 'cin' undeclared (first use in this function)
  cin>>a>>b;
  ^~~
foo.c:6:2: note: each undeclared identifier is reported only once for each function it appears in
foo.c:7:2: error: 'cout' undeclared (first use in this function)
  cout<<a+b;
  ^~~~
foo.c:9:1: error: expected ';' before '}' token
 }
 ^