/in/foo.cc: In function 'int main()':
/in/foo.cc:6:11: warning: 'a' is used uninitialized in this function [-Wuninitialized]
  cout<<b-2*a<<endl;
          ~^~
/in/foo.cc:6:12: warning: 'b' is used uninitialized in this function [-Wuninitialized]
  cout<<b-2*a<<endl;
            ^