#include<stdio.h>
int?main()
{
	int?year;
	int?month;						//該年的第幾個月
	int?day;						//該月的第幾天
	int?sum;						//該年的第多少天
	int?Jan?=?31;
	int?Feb;
	int?March?=?31;
	int?April?=?30;
	int?May?=?31;
	int?June?=?30;
	int?July?=?31;
	int?Aug?=?31;
	int?Sep?=?30;
	int?Oct?=?31;
	int?Nov?=?30;
	int?Dce?=?31;
	//
	printf("請輸入年份：\n");
	scanf_s("%d",?&year);
	if?((year?%?4?==?0?&&?year?%?100?!=?0)?||?year?%?400?==?0)				//判斷是否閏年
	{
		Feb?=?29;
	}
	else
	{
		Feb?=?28;
	}
	//																		//選擇并判斷該月份的天數
	printf("請輸入月份：\n");
	scanf("%d",?&month);
	switch?(month)
	{
	case?1:Jan;?break;
	case?2:Feb;?break;
	case?3:March;?break;
	case?4:April;?break;
	case?5:May;?break;
	case?6:June;?break;
	case?7:July;?break;
	case?8:Aug;?break;
	case?9:Sep;?break;
	case?10:Oct?:?break;
	case?11:Nov;?break;
	case?12:Dce;?break;
	default:printf("%s",?"請輸入正確的月份！\n");
	}
	//
	printf("請輸入日期：\n");
	scanf("%d",?&day);
	if?(month?=?1?)
	{
		if?(day?<=31)
		sum?=?day;
	}
	else
	{
		printf("請輸入正確的日期！\n");
	}
	if?(month?=?2)
	{
		if?(day?<=?29||day?<=28)
		sum?=?Jan?+?day;
	}
	else
	{
		printf("請輸入正確的日期！\n");
	}
	if?(month?=?3)
	{
		if?(day?<=?31)
		sum?=?Jan?+?Feb?+?day;
	}
	else
	{
		printf("請輸入正確的日期！\n");
	}
	if?(month?=?4)
	{
		if?(day?<=?30)
		sum?=?Jan?+?Feb?+?March?+?day;
	}
	else
	{
		printf("請輸入正確的日期！\n");
	}
	if?(month?=?5)
	{
		if?(day?<=?31)
		sum?=?Jan?+?Feb?+?March?+?April?+?day;
	}
	else
	{
		printf("請輸入正確的日期！\n");
	}
	if?(month?=?6)
	{
		if?(day?<=?30)
		sum?=?Jan?+?Feb?+?March?+?April?+?May?+?day;
	}
	else
	{
		printf("請輸入正確的日期！\n");
	}
	if?(month?=?7)
	{
		if?(day?<=?31)
		sum?=?Jan?+?Feb?+?March?+?April?+?May?+?June?+?day;
	}
	else
	{
		printf("請輸入正確的日期！\n");
	}
	if?(month?=?8)
	{
		if?(day?<=?31)
		sum?=?Jan?+?Feb?+?March?+?April?+?May?+?June?+?July?+?day;
	}
	else
	{
		printf("請輸入正確的日期！\n");
	}
	if?(month?=?9)
	{
		if?(day?<=?30)
		sum?=?Jan?+?Feb?+?March?+?April?+?May?+?June?+?July?+?Aug?+?day;
	}
	else
	{
		printf("請輸入正確的日期！\n");
	}
	if?(month?=?10)
	{
		if?(day?<=?31)
		sum?=?Jan?+?Feb?+?March?+?April?+?May?+?June?+?July?+?Aug?+?Sep?+?day;
	}
	else
	{
		printf("請輸入正確的日期！\n");
	}
	if?(month?=?11)
	{
		if?(day?<=?30)
		{
			sum?=?Jan?+?Feb?+?March?+?April?+?May?+?June?+?July?+?Aug?+?Sep?+?Oct?+?day;
		}
		else
		{
			printf("請輸入正確的日期！\n");
		}
	}

	if?(month?=?12)
	{
		if?(day?<=?31)
		{
			sum?=?Jan?+?Feb?+?March?+?April?+?May?+?June?+?July?+?Aug?+?Sep?+?Oct?+?Dce?+?day;
		}
		else
		{
			printf("請輸入正確的日期！");
		}
	}

	//
	printf("%d年的%d月%d日是該年的第%d天",?year,month,day,sum);
	return?0;
}

每次輸入的月份都會輸出為12，請問一下哪邊出了問題？