【C語言】結構體判斷一個日期是該年的第幾天

#include <stdio.h>
#include <stdlib.h>

struct date {
    int year;
    int month;
    int day;
} date;

int main() {
    int sum = 0,tag;
    printf("請輸入年月日：\n");
    scanf("%d,%d,%d", &date.year, &date.month, &date.day);
    switch (date.month) {   //先計算月份前面的月份有多少天（不考慮閏年）
    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("the month error");
        exit(1);
    }
    //這裏可以寫一些日的合法判斷
    sum += date.day;  //加上本月的日期數
    if(date.year% 400 == 0 || (date.year % 4==0 && date.year % 100 != 0 ))  //閏年
        tag = 1;
    else
        tag = 0;
    if(tag == 1 && date.month > 2)   //是閏年  月份大於2月   天數加一天
        sum++;
    printf("這天是當年的第 %d 天。\n",sum);
    return EXIT_SUCCESS;
}