/in/foo.cc: In function 'int sum(int, int)':
/in/foo.cc:10:9: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return ans; 
         ^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:29:17: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
    cout<<sum(l,r)<<endl;
                 ^