#include <iostream>
#include <cctype>
#include <cstdlib>
 
using namespace std;
 
class DigitalTime
{
public:
	friend bool operator ==(const DigitalTime& time1, const DigitalTime& time2);
 
	DigitalTime(int the_hour, int the_minute);
 
	DigitalTime();
 
	void advance(int minutes_added);
 
	void advance(int hours_added, int minutes_added);
 
	void interval_since(const DigitalTime& a_previous_time, int& hours_in_interval, int& minutes_in_interval);
 
	friend istream& operator >>(istream& ins, DigitalTime& the_object);
 
	friend ostream& operator <<(ostream& outs, const DigitalTime& the_object);
private:
	int hour;
	int minute;
};
 
int main()
{
	DigitalTime clock, old_clock, current(5, 45), previous(2, 30);
	int hours, minutes;
	string holdprogram;
 
	cout << "Enter the time in 24-hour notation: ";
	cin >> clock;
 
	old_clock = clock;
	clock.advance(15);
 
	if (clock == old_clock)
		cout << "Something is wrong.";
		cout << "You entered " << old_clock << endl;
		cout << "15 minutes later the time will be "
			 << clock << endl;
 
	clock.advance(2, 15);
	cout << "2 hours and 15 minutes after that\n"
		 << "the time will be "
		 << clock << endl;
 
	current.interval_since(previous, hours, minutes);
	cout << "The time interval between " << previous
		 << " and " << current << endl
		 << "is " << hours << " hours and "
		 << minutes << " minutes.\n";
 
	cin >> holdprogram;
 
	return 0;
}
 
void read_hour(istream& ins, int& the_hour);
 
void read_minute(istream& ins, int& the_minute);
 
int digit_to_int(char c);
 
bool operator ==(const DigitalTime& time1, const DigitalTime& time2)
{
	return (time1.hour == time2.hour && time1.minute == time2.minute);
}
 
DigitalTime::DigitalTime(int the_hour, int the_minute)
{
	if (the_hour < 0 || the_hour > 23 || the_minute < 0 || the_minute > 59)
	{
		cout << "Illegal argument to DigitalTime constructor.";
		exit(1);
	}
	else
	{
		hour = the_hour;
		minute = the_minute;
	}
}
 
DigitalTime::DigitalTime() : hour(0), minute(0)
{
 
}
 
void DigitalTime::advance(int minutes_added)
{
	int gross_minutes = minute + minutes_added;
	minute = gross_minutes%60;
 
	int hour_adjustment = gross_minutes/60;
	hour = (hour + hour_adjustment)%24;
}
 
void DigitalTime::advance(int hours_added, int minutes_added)
{
	hour = (hour + hours_added)%24;
	advance(minutes_added);
}
 
void DigitalTime::interval_since(const DigitalTime& a_previous_time, int& hours_in_interval, int& minutes_in_interval)
{
	// i'm stuck here
}
 
ostream& operator <<(ostream& outs, const DigitalTime& the_object)
{
	outs << the_object.hour << ':';
	if (the_object.minute < 10)
		outs << '0';
		outs << the_object.minute;
		return outs;
}
 
istream& operator >>(istream& ins, DigitalTime& the_object)
{
	read_hour(ins, the_object.hour);
	read_minute(ins, the_object.minute);
	return ins;
}
 
int digit_to_int(char c)
{
	return ( static_cast<int>(c) - static_cast<int>('0') );
}
 
void read_minute(istream& ins, int& the_minute)
{
	char c1, c2;
	ins >> c1 >> c2;
 
	if (!(isdigit(c1) && isdigit(c2)))
	{
		cout << "Error illegal input to read_minute\n";
		exit(1);
	}
 
	the_minute = digit_to_int(c1)*10 + digit_to_int(c2);
 
	if (the_minute < 0 || the_minute > 59)
	{
		cout << "Error illegal input to read_minute\n";
		exit(1);
	}
}
 
void read_hour(istream& ins, int& the_hour)
{
	char c1, c2;
	ins >> c1 >> c2;
 
	if ( !( isdigit(c1) && (isdigit(c2) || c2 == ':') ) )
	{
		cout << "Error illegal input to read_hour\n";
		exit(1);
	}
 
	if(isdigit(c1) && c2 == ':')
	{
		the_hour = digit_to_int(c1);
	}
	else
	{
		the_hour = digit_to_int(c1)*10 + digit_to_int(c2);
		ins >> c2;
		if (c2 != ':')
		{
			cout << "Error illegal input to read_hour\n";
			exit(1);
		}
	}
 
	if (the_hour < 0 || the_hour > 23)
	{
		cout << "Error illegal input to read_hour\n";
		exit(1);
	}
}

void DigitalTime::interval_since(const DigitalTime& a_previous_time, int& hours_in_interval, int& minutes_in_interval)
{
	int hours_dif;
	int minutes_dif;
	hours_dif=abs(hour-a_previous_time.hour);
	minutes_dif=abs(minute-a_previous_time.minute);
	if(minutes_dif >= 60) {
		hours_dif+=int(minutes_dif/60);
		minutes_dif=minutes_dif%60;
	}
	hours_in_interval = hours_dif;
	minutes_in_interval = minutes_dif;
 
}