请大家帮忙找错误

  switch(month)

    {

    case 1:sum=0;break;

    case 2:sum=31;break;

    case 3:sum=28+31;break;

    case 4:sum=31+28+31;break;

    case 5:sum=30+28+31+31;break;

    case 6:sum=31+30+28+31+31;break;

    case 7:sum=30+31+30+28+31+31;break;

    case 8:sum=31+30+31+30+28+31+31;break;

    case 9:sum=31+31+30+31+30+28+31+31;break;

    case 10:sum=30+31+31+30+31+30+28+31+31;break;

    case 11:sum=31+30+31+31+30+31+30+28+31+31;break;

    case 12:sum=30+31+30+31+31+30+31+30+28+31+31;break;

  }

     if(year%4==0&&year%100!=0||year%400==0)

       {

           sum=sum+1+day;

       }

    else{

        sum=sum+day;

    }