foo.cc: In function 'int rn(int)':
foo.cc:40:27: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if(year%4==0||year%400==0&&year%100!=0)
                ~~~~~~~~~~~^~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:20:6: warning: 'yearday' may be used uninitialized in this function [-Wmaybe-uninitialized]
   sum=sum+yearday;
   ~~~^~~~~~~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。