/in/foo.cc: In function 'int main()':
/in/foo.cc:28:17: warning: 'R' may be used uninitialized in this function [-Wmaybe-uninitialized]
  reverse(a+L,a+R+1);
              ~~~^~
/in/foo.cc:28:11: warning: 'L' may be used uninitialized in this function [-Wmaybe-uninitialized]
  reverse(a+L,a+R+1);
          ~^~