C语言日期倒计时

#include<stdio.h>
#include<time.h>

//判断是否是闰年
int leap(int year)
{
    if(year%4==0&&year%100!=0) return 1;
    else if(year%400==0) return 1;
    else return 0;
}

//返回某年某月的天数
int monthdays(int year, int month)
{
    if(month==1||month==3||month==5||month==7||month==8||month==10||month==12)
        return 31;
    else if(leap(year)==1&&month==2) return 29;
    else if(month==2) return 28;
    else return 30;
}

int sumdays(int year0,int month0,int day0,int year,int month,int day)
{
    int sum=0, i, j, k, days;
    for(i=year0; i<year; i++)
    {
        if(leap(i)) days = 366;
        else days = 365;
        sum = sum+days;
    }
    for(j=1; j<month0; j++)
        sum = sum - monthdays(year0,j);
    sum = sum-day0;
    for(k=1; k<month; k++)
        sum = sum + monthdays(year,k);
    sum = sum + day;
    return sum;
}

int main()
{
    time_t nowtime;
    struct tm *timeinfo;
    time(&nowtime);
    timeinfo = localtime(&nowtime);
    int year, month, day, year0, month0, day0, sumday;
    year0 = timeinfo->tm_year + 1900;
    month0 = timeinfo->tm_mon + 1;
    day0 = timeinfo->tm_mday;
    printf("*****放假倒计时*****\n\n");
    //year0 =1990; month0=1; day0=1;
    printf("请分别输入放假日期=>年、月、日：");
    scanf("%d %d %d", &year,&month,&day);
    printf("今天是%d年%d月%d日\n\n", year0, month0, day0);
    printf("\n放假日期为%d年%d月%d日\n\n", year, month, day);
    sumday = sumdays(year0,month0,day0,year,month,day);
    printf("距离放假还有【%d】天\n\n", sumday);
    return 0;
}