I have the following code which is working properly, what I'm looking to do is add an additional function to it, but I'm getting stuck.

What I need to do is add a function to my class called DigitalTime::interval_since(const DigitalTime& a_previous_time, int& hours_in_interval, int& minutes_in_interval)

What this function does is computes the time interval between two values of type DigitalTime. One of the values of type DigitalTime is the object that calls the member function interval_since, and the other value of type DigitalTime is given as the first argument.

So basically I'm looking to call it like so:

DigitalTime current(5, 45), previous(2, 30);

int hours, minutes;

current.interval_since(previous, hours, minutes);

cout << "The time interval between " << previous

<< " and " << current << endl

<< "is " << hours << " hours and "

<< minutes << " minutes.\n";

I'm really having trouble figuring out how to create this function, any help would be most appreciated.

Here is the full code if it helps:

```
#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);
}
}
```