設計程式，從 鍵盤輸入年月日三個變數year,month,day，計算該日是該年第幾天

#include<stdio.h>
int main()
{
	int year, month, day,n,i,sum=0;
	scanf("%d,%d,%d", &year, &month, &day);
	int a[13] = { 0,31,28,31,30,31,30,31,31,30,31,30,31};
	if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0)
		a[2] = 29;
	if (month < 1 || month>12)
		printf("月份錯誤\n");
	n = month;
	if (day<1 || day>a[n])
		printf("天數錯誤\n");

	else
	{
		for (i = 0; i < n; i++)
			sum = sum + a[i];
		sum += day;
		printf("%d\n", sum);
	}

}