如何计算日期差

#include<iostream>
#include<math.h>
using namespace std;
struct Date
{
    int y;//year
    int m;//month
    int d;//day in month
}date1,date2;
bool isLeap(int y)//判断是否是闰年
{
    return y % 4 == 0 && y % 100 != 0 || y % 400 == 0;//真返回为1，假为0
}
int daysOfMonth(int y, int m)
{
    int day[12] = { 31,28,31,30,31,30,31,31,30,31,30,31 };
    if (m != 2)
        return day[m - 1];
    else
        return 28 + isLeap(y);
}
int daysOfDate(Date d)//计算一共的天数
{
    long days = d.d;  //初始化天数
    for (int y = 1; y < d.y; y++)//计算年
        days += 365 + isLeap(y);
    for (int m = 1; m < d.m; m++)//计算月
        days += daysOfMonth(d.y, m);
    return days;
}
int main() {
    char date[20]; char month[3] = { 0 }; char year[3] = { 0 }; char day[3] = {0};
    char Month[13][20] = { "January", "February", "March", "Apri", "May"," June"," July", "August", "September", "October", "November","December" }; // 储存月份
    int i = 0; 
    cin >> date;
    for (i = 0; i < 2; i++)year[i] = date[i];
    for (i = 0; i < 2; i++)month[i] = date[3 + i];
    for (i = 0; i < 2; i++)day[i] = date[6 + i];
    date1.y = atoi(year);
    date1.m = atoi(month);
    date1.d = atoi(day);
    if (date1.y > 12) {  //唯一日期表示
        cout <<Month[date1.m - 1] << " " << date1.d << ", "<<date1.y<<endl;
    }
    else {
        for (i = 0; i < 2; i++)month[i] = date[0 + i];
        for (i = 0; i < 2; i++)day[i] = date[3 + i];
        for (i = 0; i < 2; i++)year[i] = date[6 + i];
        date2.y = atoi(year);
        date2.m = atoi(month);
        date2.d = atoi(day);
        cout << abs(daysOfDate(date1) - daysOfDate(date2)) << endl;
    }
    return 0;
}