foo.cc:38:9: error: ISO C++ forbids declaration of ‘addNode’ with no type [-fpermissive]
   38 |         addNode(int x){
      |         ^~~~~~~
foo.cc:49:9: error: ISO C++ forbids declaration of ‘output’ with no type [-fpermissive]
   49 |         output(){
      |         ^~~~~~
foo.cc:58:9: error: ISO C++ forbids declaration of ‘destroy’ with no type [-fpermissive]
   58 |         destroy(){
      |         ^~~~~~~
foo.cc: In member function ‘int LinkList::addNode(int)’:
foo.cc:47:9: warning: no return statement in function returning non-void [-Wreturn-type]
   47 |         }
      |         ^
foo.cc: In member function ‘int LinkList::output()’:
foo.cc:56:9: warning: no return statement in function returning non-void [-Wreturn-type]
   56 |         }
      |         ^
foo.cc: In member function ‘int LinkList::destroy()’:
foo.cc:65:9: warning: no return statement in function returning non-void [-Wreturn-type]
   65 |         }
      |         ^