foo.cc: In function ‘int main()’:
foo.cc:8:17: error: ‘S’ was not declared in this scope
    8 |                 S=A;
      |                 ^
foo.cc:8:19: error: ‘A’ was not declared in this scope
    8 |                 S=A;
      |                   ^
foo.cc:12:17: error: ‘d’ was not declared in this scope
   12 |                 d=c;
      |                 ^
foo.cc:13:15: error: ‘d’ was not declared in this scope
   13 |         cout<<d;
      |               ^