/in/foo.c: In function 'main':
/in/foo.c:6:5: error: 'cin' undeclared (first use in this function)
    6 |     cin<<a <<b <<c<<endl;
      |     ^~~
/in/foo.c:6:5: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:6:10: error: 'a' undeclared (first use in this function)
    6 |     cin<<a <<b <<c<<endl;
      |          ^
/in/foo.c:6:14: error: 'b' undeclared (first use in this function)
    6 |     cin<<a <<b <<c<<endl;
      |              ^
/in/foo.c:6:18: error: 'c' undeclared (first use in this function)
    6 |     cin<<a <<b <<c<<endl;
      |                  ^
/in/foo.c:6:21: error: 'endl' undeclared (first use in this function)
    6 |     cin<<a <<b <<c<<endl;
      |                     ^~~~
/in/foo.c:7:10: error: 'd' undeclared (first use in this function)
    7 |     cin<<d;
      |          ^
/in/foo.c:8:9: error: 'cout' undeclared (first use in this function)
    8 |         cout<<c+d endl;
      |         ^~~~
/in/foo.c:8:18: error: expected ';' before 'endl'
    8 |         cout<<c+d endl;
      |                  ^~~~~
      |                  ;