How do assign an overall variable for several inputs?

Question

I am new to C++. I am facing a problem. I want to have 2 different dates (DD/MM/YYYY) How do I assign an overall variable for the first chunk and another one for the 2nd chunk?

For example:

First Day of date: 2
First Month ""   : 5
First year ""    : 1985
-------
Second ""
second ""
second ""
--------

if both are the same dates the output will be "Both are equal" else the greater will be mentioned "Date ... is greater"

I appreciate the help in advance.

#include <iostream>
using namespace std;


int main()
{
    //This should be my first chunk
    
    int first_date;
    cout << "first day: ";
    cin >> first_y;


    int first_month;
    cout << "first month: ";
    cin >> first_month;


    int first_year;
    cout << "first year: ";
    cin >> first_year;  
}

Define a structure that represents a date. Use two of those. (And get a [good book](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list).) — molbdnilo, Oct 27 '21 at 16:06

Ted Lyngmo · Answer 1 · 2021-10-27T16:28:04.763

You could create a struct to keep the day, month and year:

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

You could also add member functions to that struct to simplify the input process:

struct date_t {
    // ... the above member variables goes here ...

    void enter_day(const char* prompt) {
        std::cout << prompt << " day: ";
        std::cin >> day;
    }
    void enter_month(const char* prompt) {
        std::cout << prompt << " month: ";
        std::cin >> month;
    }
    void enter_year(const char* prompt) {
        std::cout << prompt << " year: ";
        std::cin >> year;
    }
    void enter_all(const char* prompt) {
         enter_day(prompt);
         enter_month(prompt);
         enter_year(prompt);
    }
};

If you now create an array of date_t:

date_t dates[2];

you can just call the enter_all() function for both:

dates[0].enter_all("first");
dates[1].enter_all("second");

Now, everything related to the first date will be in dates[0], like dates[0].day and everything related to the second date will be in dates[1], like dates[1].year etc.

To compare two date_t's you can add comparison operators. Here are a few examples. You should be able to use these to create the missing operators, like operator<= etc. If you use C++20, you could implement operator<=>.

// compare two `date_t`s to see if they are equal:
bool operator==(const date_t& lhs, const date_t& rhs) {
    return lhs.day == rhs.day &&
           lhs.month == rhs.month &&
           lhs.year == rhs.year;
}

// check if the left date is before the right date
bool operator<(const date_t& lhs, const date_t& rhs) {
    if(lhs.year != rhs.year) return lhs.year < rhs.year;
    if(lhs.month != rhs.month) return lhs.month < rhs.month;
    return lhs.day < rhs.day;
}

// check if the left date is after the right date
bool operator>(const date_t& lhs, const date_t& rhs) {
    return rhs < lhs; // use the above operator<
}

With that you could do:

if(dates[0] == dates[1]) std::cout << "they are equal\n";
// or...
if(dates[0] < dates[1]) std::cout << "first < second\n";
// or...
if(dates[0] > dates[1]) std::cout << "first > second\n";

Jason · Accepted Answer · 2021-10-27T16:43:58.880

The below program shows what you want:

#include <iostream>

struct Date
{
    //always always initialize built in type in block/local scope
    int date = 0, month = 0, year = 0; // by default public 
    
    
    //default constructor 
    Date() = default;
    
    //lets overload operator= for comparing two Date types as you desire
    friend bool operator==(const Date &lhs, const Date &rhs);
    friend bool operator!=(const Date &lhs, const Date &rhs);
    
    //overload operator>> for taking input from user 
    friend std::istream& operator>>(std::istream &is, Date &rhs);
};
bool operator==(const Date &lhs, const Date &rhs)
{
    return lhs.date == rhs.date &&
           lhs.month == rhs.month &&
           lhs.year == rhs.year;
}
bool operator!=(const Date &lhs, const Date &rhs)
{
    return !(lhs == rhs);
}
std::istream& operator>>(std::istream &is, Date &rhs)
{
    std::cout<<"Enter date: ";
    //take date as input from user
    std::cin >> rhs.date;
    
    std::cout<<"Enter month: ";
    //take month as input from user
    std::cin >> rhs.month;
    
    std::cout<<"Enter year: ";
    //take year as input from user
    std::cin >> rhs.year;
    
    //check if input succedded
    if(!is)
    {
        rhs = Date();
    }
    return is;
}
int main() 
{
    
    //create first Date 
    struct Date d1;
    
    std::cin >> d1;//take input from user
    
    //create second Date 
    struct Date d2;
    
    std::cin >> d2;//take input from user
    
    //lets check if dates d1 and d2 entered by user are equal or not
    std::cout<<"The dates d1 and d2 are: "<<(d1==d2? "equal": "not equal")<<std::endl;
    
    
    
    return 0;
}

How do assign an overall variable for several inputs?

2 Answers2