// Variables for calculation.
	int timeDif; int startTime; int endTime;
	int startHour; int startMin; int startSec;
	int endHour; int endMin; int endSec;
	int startDay; int endDay;

	// Part of the Extra Credit. Finding the day values.
	startDay = stoi(startDateValue.substr(6, 2));
	endDay = stoi(dateValue.substr(6, 2));

	// Start time individual values from string to integer.
	startHour = stoi(startDateValue.substr(8, 2));
	startMin = stoi(startDateValue.substr(10, 2));
	startSec = stoi(startDateValue.substr(12, 2));

	// Start time in seconds format.
	startTime = (((startHour * 60) + startMin) * 60) + startSec;

	// End time individual values from string to integer.
	endHour = stoi(dateValue.substr(8, 2));
	endMin = stoi(dateValue.substr(10, 2));
	endSec = stoi(dateValue.substr(12, 2));

	// End time in seconds format.
	endTime = (((endHour * 60) + endMin) * 60) + endSec;

	// Second part of extra credit.
	// If the days do not equal each other,
	// a days worth of seconds is added to the
	// end time to account for calls going over night.
	if (startDay != endDay) {
		endTime = endTime + 86400;
	}

	// The final calculation of the duration.
	timeDif = endTime - startTime;

	return timeDif;