//A program to compare two dates and compute the number of days between them
#include <iostream>
using namespace std;

//Function prototypes
bool IsLeapYear (int);
int DayNumber(int, int, bool);
int diff(int, int, int, int, bool);

//Constants used by function DayNumber
const int JAN = 0;
const int FEB = 31;
const int MAR = 59;
const int APR = 90;
const int MAY = 120;
const int JUN = 151;
const int JUL = 181;
const int AUG = 212;
const int SEP = 243;
const int OCT = 273;
const int NOV = 304;
const int DEC = 334;

int main () 
{
	int month1, month2;			//Input
	int date1, date2;			//Input
	int year1, year2;			//Input
	char slash;					//Input
	bool isLeap1, isLeap2;		//Variable - true if leap year
	isLeap1 = false;			//Initialise bool variables
	isLeap2 = false;			//Do I need to do this?
	int number1, number2;		//Variable - numbered date (1 - 365) (or 1 - 366 in leap year)
	int result;					//Variable - difference between two dates in days
	
	//Get input
	cout << "Please enter two dates in numeric form (i.e. 1/1/2001). Please enter first date: ";
	cin >> month1 >> slash >> date1 >> slash >> year1;
	cout << "Enter the second date: ";
	cin >> month2 >> slash >> date2 >> slash >> year2;
	   
	//Find out if year 1 is a leap year
	isLeap1 = IsLeapYear (year1);
	
	//Compute numbered date for year 1
	number1 = DayNumber (month1, date1, isLeap1);
	
	//Find out if year 2 is a leap year
	isLeap2 = IsLeapYear (year2);
	
	//Compute numbered date for year 2
	number2 = DayNumber (month2, date2, isLeap2);
	
	//Compute difference in days between the two dates
	result = diff(number1, number2, year1, year2, isLeap1);
	
	//Output the result
	cout << "The difference between " << month1 << slash << date1 << slash << year1
		<< " and " << month2 << slash << date2 << slash << year2 << " is " << result << " days." << endl;

    return 0;
}

//A function to determine if a given year is a leap year
bool IsLeapYear (int year)	//WaltP, I used your version as it was better than mine!
{	
    bool rtn;

    rtn = false;            // Assume this is not a leapyear

	
    if ((year % 400) == 0)  // if true it is a leap year 
    {                       // every 400 years....
        rtn = true;
    }
    else                    // otherwise
    if ((year % 100) == 0)  // if true it's not a leap year
    {                       // every 100 years, but not 400
        rtn = false;        // not needed but it's better to have a statement
    }
    else                    // otherwise
    if ((year % 4) == 0)    // if true it is a leap year 
    {                       // every 4 years, but not every 100 years
        rtn = true;
    }
	return rtn;             // Always return a value
}

//A function to compute the numbered date from 1 - 365 (1 - 366 if leap year)
int DayNumber (int month, int date, bool isLeap)	//Should I declare these parameters as constants?
{
	int number;				//Local variable - result of computation
	number = date;			//Puts value of date in number
	
	switch (month)			//Depending on what month is input
	{
		case 1:				//If January
			number += JAN;	//Add offset determined by constants declared prior to main
		break;
		case 2:				//If February
			number += FEB;	//Add offset
		break;
		case 3:				//etc.
			number += MAR;
		break;
		case 4:
			number += APR;
		break;
		case 5:
			number += MAY;
		break;
		case 6:
			number += JUN;
		break;
		case 7:
			number += JUL;
		break;
		case 8:
			number += AUG;
		break;
		case 9:
			number += SEP;
		break;
		case 10:
			number += OCT;
		break;
		case 11:
			number += NOV;
		break;
		case 12:
			number += DEC;
		break;
		default:							//If none of the above
			cout << "Error!" << endl;
	}										//End of switch(month)
	if ((isLeap == true) && (month > 2))	//If both a leap year and later than February
	{
		number++;							//Add one day
	}   	
	return number;							//Returns the computed date number
}											//End DayNumber function

//A function to compute the difference in days between two dates
int diff(int number1, int number2, int year1, int year2, bool isLeap1)
{
	int result;								//Local variable - result of computation
	if (year1 == year2)						//If years are the same
	{
		if(number1 > number2)				//Determine if the computed dates are out of order
		{									//Reverse dates
			int temp;
			temp = number1;
			number1 = number2;
			number2 = temp;
		}									//Dates are now in proper order
		result = number2 - number1;			//Compute the result as difference
	}
	else									//Otherwise (if years are different)
	{
		if(year1 > year2)					//Determine if years are in reverse order
		{
			int temp;						//If so, first reverse years
			temp = year1;
			year1 = year2;
			year2 = temp;
			temp = number1;					//then also reverse computed dates to correspond with years
			number1 = number2;
			number2 = temp;
		}									//Years and dates are now in proper order
		result = 365 - number1;				//Result gets 365 minus the lowest date
		
		isLeap1 = IsLeapYear(year1);		//Calls function to determine if the lowest year is a leap year
		if (isLeap1 == true)				//If the lowest year is a leap year
		{
			result++;						//Add one day to the result
		}
		year1++;							//Increment lowest year

		while (year1 < year2)				//Loop repetition condition - lowest year must be less than highest year
		{									//While true
			result += 365;					//Add 365 days to result
			isLeap1 = IsLeapYear(year1);	//Determine if current year is leap year
				if (isLeap1 == true)		//If true
				{
					result++;				//Add one day to result
				}	
			year1++;						//Increment current year
		}									//End while loop
		result += number2;					//After while loop is finished, add number of days in year two to result
	}
	return result;							//Return result
}
	

Please enter two dates in numeric form (i.e. 1/1/2001). Please enter first date: 1/1/1752
Enter the second date: 12/31/1752
The difference between 1/1/1752 and 12/31/1752 is 365 days.

#include <iostream>
#include <stdexcept>
#include <ctime>

using namespace std;

class Time
{
public:
protected:
private:

};
class Date
{
public:
    Date()  // initializes to "now"
    {
        time_t now;
        time( &now );
    }
    Date( int month, int day, int year, bool AD=true ) :
    m_month_component( month ),
    m_day_component( day ),
    m_year_component( year ),
    m_bIsAD( AD )
    {
        if( year <= 0 )
        {
            throw new out_of_range( "Illegal Year Value" );
        }
    }
    Date( const Date& rhs )
    {
        m_month_component = rhs.m_month_component;
        m_day_component   = rhs.m_day_component;
        m_year_component  = rhs.m_year_component;
        m_bIsAD           = rhs.m_bIsAD;
    }
    // put dtor here...

protected:
private:  // private because we should probably not be derived...
    int m_month_component;
    int m_day_component;
    int m_year_component;
    bool m_bIsAD;
    Time m_time;
};