foo.cc: In function 'int main()':
foo.cc:9:13: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
    if(n%4==0&&n%100!=0||n%400==0) cout<<29;
       ~~~~~~^~~~~~~~~~

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