C语言学习，通过输入年月日计算出这天是这年的第几天

#include<stdio.h>
int main()
{
  int day,month,year,sum;
  printf("请输入年月日（中间用‘，’隔开）\n");
  scanf("%d,%d,%d",&year,&month,&day);
  switch (month) 
  {
    case 1:
      sum=0;
      break;
    case 2:
      sum=31;
      break;
    case 3:
      sum=60;
      break;  
      case 4:
      sum=91;
      break;
    case 5:
      sum=121;
      break;
    case 6:
      sum=152;
      break;
    case 7:
      sum=182;
      break;
    case 8:
      sum=213;
      break;
    case 9:
      sum=244;
      break;
    case 10:
      sum=274;
      break;
    case 11:
      sum=304;
      break;
    case 12:
      sum=334;
      break;            
    default:
      printf("月份输入错误");
      break;
  }
  if((year%4==0 && year%4!=0)||(year%400==0))
    printf("这是%d年的第%d天\n",year,sum+day);
  else
      printf("这是%d年的第%d天\n",year,sum+day-1);
  return 0;
}