未正确检查日期结构

I have some C++ code:

我有一些C ++代码:

#include <bjarne/std_lib_facilities.h>

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

Date get_date();
Date get_birth_date();
int days_in_month (int month);
bool is_valid_date (const Date& date);
bool is_before (const Date& date1, const Date& date2);

int main()
{
    cout << "Welcome to Age Calculator!\n"; 
    Date current;
    current = get_date();
    cout << "Would you like to see how old you are (y/n)?";
    char answer, slash;
    cin >> answer;
    Date birthday;
    if(answer == 'y'){
        birthday = get_birth_date();
        bool valid = is_valid_date (birthday);
        bool before = is_before (current,birthday);
        while(!valid && !before){
            cout << "Invalid birth date?  Please re-enter: ";
            cin >> birthday.month >> slash >> birthday.day >> slash >> birthday.year;
            valid = is_valid_date (birthday);
            before = is_before (current,birthday);
        }
        cout << "Your birthday is: " << birthday.month << "/" << birthday.day << "/" << birthday.year << "\n";
    }
    else
    cout << "You are so chicken! \n";    
}

Date get_date()
{
    cout << "Please enter today's date (mm/dd/yyyy): ";
    Date today; 
    char slash;
    cin >> today.month >> slash >> today.day >> slash >> today.year;
    bool valid = is_valid_date (today);
    while(!valid){
        cout << "Invalid date?  Please re-enter: ";
        cin >> today.month >> slash >> today.day >> slash >> today.year;
        valid = is_valid_date (today);
    }
    cout << "Date entered was: " << today.month << "/" << today.day << "/" << today.year << "\n";
    return today;
}

Date get_birth_date()
{
    cout << "Please enter your birth date (mm/dd/yyyy): ";
    Date birth; 
    char slash;
    cin >> birth.month >> slash >> birth.day >> slash >> birth.year;
    return birth;
}

int days_in_month (int month)
{
    int month31[7] = {1,3,5,7,8,10,12};
    for(int i = 0; i < 7; i++){
        if(month == month31[i])
            return 31;
    }
    int month30[4] = {4,6,9,11};
    for(int i = 0; i < 4; i++){
        if(month == month30[i])
            return 30;
    }
    if(month == 2)
        return 28;
}

bool is_valid_date (const Date& date)
{
    int months[12] = {1,2,3,4,5,6,7,8,9,10,11,12};
    int days = 0; 
    for(int i = 0; i < 12; i++){
        if(date.month == months[i]){
            days = days_in_month (date.month);
            if(date.day <= days && date.day > 1){
                return true;
            }

    }
    return false;
}

bool is_before (const Date& date1, const Date& date2)
{
    cout << date1.day << " " << date2.day; 
    if(date2.year < date1.year){
        return true;
    }
    else if(date2.year == date1.year)
    {
        cout << "-";
        if(date2.month < date1.month)
            return true;
        else if(date2.month == date1.month){
            if(date2.day <= date1.day)
                return true;
        }
        else
            return false;

    }
    return false;
}
#include