foo.c: In function ‘main’:
foo.c:4:5: error: ‘cin’ undeclared (first use in this function)
    4 |     cin>>a>>b;
      |     ^~~
foo.c:4:5: note: each undeclared identifier is reported only once for each function it appears in
foo.c:5:9: error: ‘cout’ undeclared (first use in this function)
    5 |         cout<<a+b;
      |         ^~~~