/in/foo.cc: In function 'int main()':
/in/foo.cc:5:36: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  for(int i=y1;i<=y2;i++) a+=(i%4==0&&i%100!=0||i%400==0);
                              ~~~~~~^~~~~~~~~~
/in/foo.cc:6:14: warning: 'a' may be used uninitialized in this function [-Wmaybe-uninitialized]
  std::cout<<a;
              ^