/in/foo.cc: In function 'int main()':
/in/foo.cc:8:12: warning: unused variable 'left' [-Wunused-variable]
  int sum=0,left=0,right=n,guess;
            ^~~~
/in/foo.cc:8:19: warning: unused variable 'right' [-Wunused-variable]
  int sum=0,left=0,right=n,guess;
                   ^~~~~
/in/foo.cc:8:27: warning: unused variable 'guess' [-Wunused-variable]
  int sum=0,left=0,right=n,guess;
                           ^~~~~