C语言 输入某年某月某日输出它是这一年的第几天

知识点：复习switch case循环和if选择语句。 

#include
#include
int main()
{
 int day, month, year, sum, leap;
 printf("请输入年月日：");
 scanf_s("%d%d%d",&year,&month,&day);
 switch (month)
 {
 case 1:sum = 0; break;
 case 2:sum = 31; break;
 case 3:sum = 59; break;
 case 4:sum = 90; break;
 case 5:sum = 120; break;
 case 6:sum = 151; break;
 case 7:sum = 181; break;
 case 8:sum = 212; break;
 case 9:sum = 243; break;
 case 10:sum = 273; break;
 case 11:sum = 304; break;
 case 12:sum = 334; break;
 default:printf("date error"); break;
 }
 sum = sum + day;
 if (year % 400 == 0 || (year % 4 == 0 && year % 100 != 0))
  leap = 1;
 else
  leap = 0;
 if (leap == 1 && month > 2)
  sum++;
 printf("这是这一年的第%d天",sum);
 system("pause");
 return 0;
}