貌似弄错了  闰年的二月是29天 还有是没考虑一月的时候
不用写这个
if(Isleapyear(year))
      count--;

下面是修改的代码 呵呵
#include <stdio.h>

int Isleapyear(int year)
{
   if((year%4==0)&&(year%100!=0)||(year%400==0))
     return 1;
   else
     return 0;

}
int main()
{
    int a[12]={31,28,31,30,31,30,31,31,30,31,30,31};
    int year,month,day,count=0;
    int i;
    printf("please input the year month and the day\n");
    scanf("%d%d%d",&year,&month,&day);
    for(i=0;i<month;i++)
       count+=a[i];
    count+=day;

    if(month>=2&&Isleapyear(year))
      count++;
    printf("%d",count);


}