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Age Calculator Problem

lckwswws (8)
Hi, fellow programmers.
I am programming about an age calculator.
It's simple:
1, get the input date 'today', check if its valid
2, get the input date 'birthday', check if it's valid and before 'today'
3, calculate the difference and output.
This is a assignment due tomorrow and I have written the most of it, just needs some debugging, mostly about pass by reference. I declared date1&date2 at main and I have no idea how to call the value of them if I want to calculate them at another function. I guess I should probably declare them at struct Date, but I am not sure.
I would really appreciate it if you guys could tell me what to do.
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/************************************************************
 *
 * Project 4: How Old Are You Really?
 *
 * Author: xx
 * Date: 6 May 2015
 *
 * This is a program designed to calculates the difference 
 * between two dates, which will be expressed in terms of
 * years, months and days.
 *
 ***********************************************************/

#include <bjarne/std_lib_facilities.h>

struct Date {
    int month;
    int day;
    int year;
// Member functions
Date get_date();
Date get_birth_date();
bool is_valid_date(int year, int month, int day);
bool is_before(Date& date1, Date& date2);
Date calculate_age(Date& date1,Date& date2);
};

// Declaration
Date get_date();
Date get_birth_date();
bool is_valid_date(int year, int month, int day);
bool is_before(Date& date1, Date& date2);
Date calculate_age(Date& date1,Date& date2);

int main()
{
    Date date1 = get_date();
    Date date2 = get_birth_date();
    Date get_date();
    // Check if the date is correct
    if (! is_valid_date(year, month, day))
    error("Date is not valid.");
    // Run how old or not?
    char go_on;
    cout << "Would you like to see how old you are (y/n)?\n";
    cin >> go_on;
    if (go_on=='n'){
    cout << "You are so chicken!";
    return 0;}
    else if (go_on!='y')
    error("Please enter y for yes or n for no.");
    Date get_birth_date();
    // Is birthday valid as well?
    if (! is_valid_date(int year, int month, int day))
    error("Date is not valid.");
    // Is the birthday before 'today'?
    if (!(is_before(Date& date1, Date& date2)))
    error("Your birthday should not be later than today, terminator.");
    // Calculate and give the answer.
    Date calculate_age();
}

Date get_date()
{
    Date date1;
    cout << "Welcome to the age calculator!\n";
    cout << "Please enter today's date (mm/dd/yyyy): ";
    int m;
    int d;
    int y;
    // To ignore the '/' during reading
    char slash;
    cin >> m;
    date1.month = m;
    cin >> slash;
    cin >> d;
    date1.day = d;
    cin >> slash;
    cin >> y;
    date1.year = y;
    cout << "Date entered was "<< date1.month << "/" << date1.day << "/" << date1.year <<"\n";
}

Date get_birth_date()
{
    Date date2;
    cout << "Please enter your birth date (mm/dd/yyyy): "; 
    int m;
    int d;
    int y;
    // To ignore the '/' during reading
    char slash;
    cin >> m;
    date2.month = m;
    cin >> slash;
    cin >> d;
    date2.day = d;
    cin >> slash;
    cin >> y;
    date2.year = y;
    cout << "Your birthday is "<< date2.month << "/" << date2.day << "/" << date2.year <<"\n";
}

// Is date valid?
bool is_vaild_date(int year, int month, int day)
{
    if (day<0)
    return false;
    if (month<1 || month>12)
    return false;
    // Check if the date exists or not considering there are have
    // different days when month varies
    int days_in_month=31;
    switch (month){
    case 2:
    days_in_month=28;
    break;
    case 4: case 6: case 9: case 11:
    days_in_month=30;
    break;
    }
    if (days_in_month<day)
    return false;
    return true;
}

//Date check - is birthday before 'today'?
bool is_before(Date& date1, Date& date2)
{
    if (Date& date1.year<Date& date2.year)
    return false;
    else if (Date& date1.month<Date& date2.month)
    return false;
    else if (Date& date1.day< Date& date2.day)
    return false;
    return true;
}

// Calculation
Date calculate_age(Date& date1,Date& date2)
{
    Date date3;
    date3.day = date1.day - date2.day;
    date3.month = date1.month - date2.month;
    date3.year = date1.year - date2.month;
    if (date3.day<0){
        date3.day = 30 + date3.day;
        date3.month = date3.month - 1;
    }
    if (date3.month<0){
        date3.month = 12 + date3.day;
        date3.year = date3.year - 1;
    }
    cout <<"You are " << date3.year <<" years, "<< date3.month <<" months, and " << date3.day <<" days old.\n";
}
FlyingC (5)
Well, from my point of view, you got a lot to do to debug this program.
Here are some problem I found and some suggestion so far,
1, you can use struct Date but no need to add so many member functions in it. In this program, just use struct as an class to store data, with a constructor to initialize the y , m and d. then you can use the object of Date to calculate.

2, these functions called in main function, 
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Date get_date();
Date get_birth_date();
Date calculate_age(Date& date1,Date& date2);


There are no return statements in the functions.

3, as I see from the program, you would like to ask user to input the dates today or birthday in an string like mm/dd/yyyy, but in the function get_date() and get_birth_date, you expect user to input the month, day and year one by one.
What I suggest is write a function to parse th input from user, and check whether it is valid , then store it into the Date object. After all these done, do your calculation.

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