如何用C语言计算一年有多少天

#include <stdio.h>

int february_day_num(int year_num);
int main() 
{ 
    /* 定义需要计算的日期 */
    int year = 2008;
    //需计算的年 
    int month = 8;
    //需计算的月 
    int day = 8;
    //需计算的日 

    int february;
    int num; 
    /*使用switch来判断月对应天数*/
    switch(month)
    {
        case 1: num=day; break;
        case 2: num=31+day; break;
        case 3: num=31+day;break;
        case 4: num=31*2+day;break;
        case 5: num=31*2+30+day;break; 
        case 6: num=31*3+30+day;break;
        case 7: num=31*3+30*2+day;break;
        case 8: num=31*4+30*2+day;break;
        case 9: num=31*5+30*2+day;break;
        case 10: num=31*5+30*3+day;break;
        case 11: num=31*6+30*3+day;break;
        case 12: num=31*6+30*4+day;break;
        default: printf("一年是十二个月哦。");break; 
    }
    /*二月的天数*/
    february = february_day_num(year);
    if(year>2)
        {
            num += february;
        }
    printf("%d年%d月%d日是该年的第%d天", year, month, day, num);
    return 0;
}
/*二月的天数判断*/
int february_day_num(int year_num)
{
    if(year_num%4==0||year_num%400==0)
    {
        if(year_num%100!=0)
        {
            year_num = 29;
        }
    }
    else 
    {
        year_num = 28;
    }
    return year_num;
}