/in/foo.cc: In function 'long long int gcd(long long int, long long int)':
/in/foo.cc:12:20: error: 'b' was not declared in this scope
   return x/y*y+gcd(b,a%b);
                    ^
/in/foo.cc:12:22: error: 'a' was not declared in this scope
   return x/y*y+gcd(b,a%b);
                      ^