foo.cc: In function 'int main()':
foo.cc:11:29: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   case 2:if(y%400==0||y%4==0&&y%100!=0){
                       ~~~~~~^~~~~~~~~~
foo.cc:6:10: warning: unused variable 'd' [-Wunused-variable]
  int y,m,d;
          ^
foo.cc:7:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d",&y,&m);
  ~~~~~^~~~~~~~~~~~~~~

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