foo.cc: In member function ‘int Cn::Add1(Cn&, Cn&, Cn&)’:
foo.cc:33:9: warning: no return statement in function returning non-void [-Wreturn-type]
   33 |         }
      |         ^
foo.cc: In member function ‘int Cn::mutiply(Cn&, Cn&)’:
foo.cc:39:9: warning: no return statement in function returning non-void [-Wreturn-type]
   39 |         }
      |         ^