Calculating Julian Day Number (JDN) using C++

#include<iostream>  
#include <limits>  
using namespace std;  
  
void input_data(int &month, int &year, int &day,int &bmonth, int &byear, int &bday);  
void calculations(int month, int year, int day, int &jdn);  
void output_results(int &month, int &year, int &day, int &jdn,int d);  
void calculate_dow(int &jdn , int &dow);  
void calculate_difference_and_print(int jdn , int bjdn);  
  
void pause();  
  
int main()  
{  
   int bday;  
   int bmonth;  
   int byear;  
   int bjdn;  
   int day;  
   int month;  
   int year;  
   int jdn;  
   int dow;  
   int bdow;  
  
   input_data(month, year, day,bmonth, byear, bday);  
   // calculate JDN for the present day  
   calculations(month, year, day, jdn);  
   // calculate JDN for the Date of birth  
   calculations(bmonth, byear, bday, bjdn);  
   calculate_dow(jdn,dow);  
   calculate_dow(bjdn,bdow);  
   cout << endl;  
   output_results(month, year, day, jdn,dow);  
   output_results(bmonth, byear, bday, bjdn,bdow);  
    calculate_difference_and_print(jdn,bjdn);  
   pause();  
}  
  
  
void pause();  
  
// this module is changed to increase the functionality  
void input_data (int &month, int &year, int &day,int &bmonth, int &byear, int &bday)  
{  
   std::cout << "enter a month(jan = 1, feb = 2, etc.) : ";  
   std::cin >> month;  
   std::cout << "enter a day number(1..31) : ";  
   std::cin >> day;  
   std::cout << "enter a year using four digits : ";  
   std::cin >> year;  
   std::cout << "enter a month of your DOB(jan = 1, feb = 2, etc.) : ";  
   std::cin >> bmonth;  
   std::cout << "enter a day number of your DOB(1..31) : ";  
   std::cin >> bday;  
   std::cout << "enter a year using four digits of your DOB : ";  
   std::cin >> byear;  
}  
  
void calculations(int month, int year, int day, int &jdn)  
{  
   int a, m, y, leap_days;  
   a = (14 - month) / 12;  
   m = (month - 3) + (12 * a);  
   y = year + 4800 - a;  
   leap_days = (y / 4) - (y / 100) + (y / 400);  
   jdn = day + (((153 * m) + 2) / 5) + (365 * y) + leap_days - 32045;  
}  
  
// this module is changed to increase the functionality  
void output_results(int &month, int &year, int &day, int &jdn,int d)  
{  
   std::cout << " The JDN for " << month << "/" << day << "/" << year << " is " << jdn << "  And Day of Week is " << d <<  std::endl;  
}  
  
void calculate_dow(int &jdn , int &dow){  
    dow = ((jdn + 1) % 7 );  
}  
  
void calculate_difference_and_print(int jdn , int bjdn){  
    cout << "Diffrence between two JDNs is " << jdn - bjdn << " Days and you are also exact same days old" << endl;  
}  
  
void pause()  
  
{  
   std::cin.clear();  
   std::cin.ignore(std::numeric_limits<int>::max(), '\n');  
   std::cout << std::endl;  
   std::cout << "Press the enter key to continue . . .";  
   std::cin.get();  
}