C语言之输入年月日 判断这一天为全年的第几天

#include <stdio.h>
void main()
{
int year,month,day;
bool a;
printf("enter year\n");
scanf("%d",&year);
printf("enter month\n");
scanf("%d",&month);
printf("enter day\n");
scanf("%d",&day);
if((year%4==0&&year%100!=0)||(year%400==0))

{
printf("year is run nian \n");
switch(month)
{
case 1 :printf("today is %d",day);
case 2 :
day=+31;
printf("today is %d",day);
break;

case 3:

day=31+28+day;

printf("today is %d",day);
break;
case 4: day=30+28+30+day;
printf("today is %d",day);
break;
case 5: day=88+31+day;
printf("today is %d",day);
break;
case 6:day=88+31+30+day;
printf("today is %d",day);
break;
case 7:day=88+31+30+day+31;
printf("today is %d",day);
break;

case 8:day=88+31+30+day+31+31;
printf("today is %d",day);
break;

case 9:day=88+31+30+day+31+30+30;
printf("today is %d",day);
break;
case 10:day=88+31+30+day+31+30+30+31;
printf("today is %d",day);
break;
case 11:day=88+31+30+day+31+30+30+30+30;
printf("today is %d",day);
break;
case 12:day=88+31+30+day+31+30+30+31+31;
printf("today is %d",day);
break;

}}
}