C#中日期转换星期

//日期转换星期(基姆拉尔森公式)
private string CaculateWeekDay(int y,int m,int d)
{
//一月和二月被当作前一年的
if((m==1)||(m==2))
{
m+=12;
y--;
}
int week=(d+2*m+3*(m+1)/5+y+y/4-y/100+y/400)%7;
string weekstr="";
switch(week)
{
case 0: weekstr="星期一"; break;
case 1: weekstr="星期二"; break;
case 2: weekstr="星期三"; break;
case 3: weekstr="星期四"; break;
case 4: weekstr="星期五"; break;
case 5: weekstr="星期六"; break;
case 6: weekstr="星期日"; break;
}
return weekstr;
}