Help with classes.

[ziggypiggy]

I need help with assignment, this is what my assignment reads:

"Define a class called Class with the same data members as the Class structure above. Member functions must be added as needed: constructor to initialize a Class object and allocate memory for it when it's created (or added), to edit the information of an existing object, to display Class information, the function for calculating the GPA and a destructor to free dynamically allocated memory for each object. The destructor ensures that each and every object created will be freed. This will make it unnecessary for Quit to call a delete() function to delete all objects and free their allocated memory . The main function will still present the menu and perform the required actions, but the actions will be performed on objects - by member functions on member data."

This is the second version of the code we must write but I'm having trouble understanding what is is my professor wants?
I've written the first part already does anyone know what I have to do to modify it to what he's asking.

#include <iostream>
#include <cstdlib>
#include <sstream>
#include <string>
#include <cstring>
#include <fstream>
#include <iomanip>
#include <cstddef>

using namespace std;

#define MAX 10

struct Class {

	char title[30];

	int units;

	char grade;

};

typedef struct Class ClassType;

int bin_search(ClassType *classPointer[], int l, int r, char title[30]);

void sort(ClassType *classPointer[]);

int find_allocated_size(ClassType *classPointer[]);

void list_all_Classes(ClassType *classPointer[]);

 

int showMenu() {

	cout << "1. Add new class " << endl;

	cout << "2. Edit an existing class" << endl;

	cout << "3. Display a class" << endl;

	cout << "4. List all classes " << endl;

	cout << "5. Display GPA" << endl;

	cout << "6. Delete all classes" << endl;

	cout << "7. Quit" << endl;

	cout << "Enter selection number: ";

	int choice;

	cin >> choice;

	while (cin.fail())

	{

		cin.clear();

		cin.ignore(1000, '\n');

		cout << "Error: Please enter a number " << endl;

		cin >> choice;

	}

	return choice;

}

void add(ClassType *classPointer[]) {

	char title[30];

	int units;

	char grade;

	int content_flag = 0;

	cout << "Enter class name: ";
	std::cin.ignore(1000, '\n');
	std::cin.getline(title, sizeof(title));

	cout << "Enter number of units: ";
	cin >> units;
	
	cout << "Enter grade received: ";
	cin >> grade;
	

	for (int i = 0; i< MAX; i++) {

		if (classPointer[i] == NULL) {

			classPointer[i] = (ClassType *)malloc(sizeof(ClassType));

			strcpy_s(classPointer[i]->title, title);

			classPointer[i]->units = units;

			classPointer[i]->grade = grade;

			content_flag = 1;

			break;

		}

	}

	if (content_flag == 1) {

		cout << "Select one of the following actions:" << endl;

	}

	else {

		cout << "Class was not added." << endl;

	}

}

void edit(ClassType *classPointer[]) {

	

	list_all_Classes(classPointer);

	cout << "Please enter index to edit: " << endl;

	int user_index;

	cin >> user_index;

	if (user_index < 0 || user_index > find_allocated_size(classPointer)) {



		cout << "Index specified is out of range" << endl;

		return;

	}

	else {
		
		
		char title[30];

		int units;

		char grade;

		cout << "Editing: " << classPointer[user_index]->title << ", "
			<< classPointer[user_index]->units << " Units, Grade: "
			<< classPointer[user_index]->grade << '\n';



		cout << "Enter class name: ";
		std::cin.ignore(1000, '\n');
		std::cin.getline(title, sizeof(title));

		cout << "Enter units: ";
		cin >> units;
		cout << "Enter grade: ";
		cin >> grade;

		

		strcpy_s(classPointer[user_index]->title, title);

		classPointer[user_index]->units = units;

		classPointer[user_index]->grade = grade;

		cout << "Class modified" << endl;

	}
	cout << "Select one of the following actions: " << endl;

}

void list_all_Classes(ClassType *classPointer[]) {



	for (int i = 0; i< MAX; i++) {

		if (classPointer[i] != NULL) {

			cout << i << ". " << classPointer[i]->title << ", " << classPointer[i]->units << " Units, " << "Grade: "<< classPointer[i]->grade << endl;

		}

	}
	cout << "Select one of the following actions: " << endl;
}

void display_single_Class(ClassType *classPointer[]) {

	if (find_allocated_size(classPointer) == 0) {

		cout << "No classes added to display" << endl;

		return;

	}

	char title[30];

	cout << "Enter the class title: ";
	std::cin.ignore(1000, '\n');
	std::cin.getline(title, sizeof(title));

	sort(classPointer);

	int allocated_size = find_allocated_size(classPointer);

	int index = bin_search(classPointer, 0, allocated_size - 1, title);

	if (index == -1) {

		cout << "Class was not found" << endl;

	}

	else {

		cout << classPointer[index]->title << ", " << classPointer[index]->units << " Units, " << "Grade: " << classPointer[index]->grade << endl;

	}
	cout << "Select one of the following actions: " << endl;
}

int find_allocated_size(ClassType *classPointer[]) {

	int count = 0;

	for (int i = 0; i< MAX; i++) {

		if (classPointer[i] != NULL) {

			count++;

		}

	}

	return count;

}

void sort(ClassType *classPointer[]) {

	int n = find_allocated_size(classPointer);



	for (int i = 0; i < n - 1; i++) {



		for (int j = 0; j < n - i - 1; j++) {



			if (strcmp(classPointer[j]->title, classPointer[j + 1]->title) > 0) {

				ClassType * temp = classPointer[j];

				classPointer[j] = classPointer[j + 1];

				classPointer[j + 1] = temp;

			}

		}

	}

}

int bin_search(ClassType *classPointer[], int l, int r, char title[30])

{

	if (r >= l)

	{

		int mid = l + (r - l) / 2;

		

		if (strcmp(classPointer[mid]->title, title) == 0)

			return mid;

		

		if (strcmp(classPointer[mid]->title, title) > 0)

			return bin_search(classPointer, l, mid - 1, title);

		

		return bin_search(classPointer, mid + 1, r, title);

	}

	
	return -1;

}
void delete_all_classes(ClassType *classPointer[]) {
	for (int i = 0; i < MAX; i++) {
		if (classPointer[i] != NULL)
		{
			free(classPointer[i]); classPointer[i] = NULL;
		}
	}
	
}

int get_points_from_grade(char grade) {
	int points; switch (grade) {
	case 'A':points = 4; break;
	case 'B':points = 3; break;
	case 'C':points = 2; break;
	case 'D':points = 1; break;
	case 'F':points = 0; break;
	default: points = 0;
	}
	return points;
}


void getGPACalulation(ClassType *classPointer[]) {
	double gpa = 0.0; 
	int sum_of_the_products = 0;
	int total_number_of_units = 0;
	int n = find_allocated_size(classPointer);
	for (int i = 0; i < n; i++) 
	{ 
	total_number_of_units += classPointer[i]->units; 
	int points = get_points_from_grade(classPointer[i]->grade); 
	sum_of_the_products += classPointer[i]->units * points;
	}
	if (total_number_of_units != 0) { 
		gpa = sum_of_the_products / double(total_number_of_units);
	} 
	cout << "GPA = " << gpa << endl;

}


int main() {

	ClassType *classPointer[MAX];

	for (int i = 0; i< MAX; i++) {

		classPointer[i] = NULL;

	}

	int choice;

	do {

		choice = showMenu();

		switch (choice) {

		case 1:

			add(classPointer);

			break;

		case 2:

			edit(classPointer);

			break;

		case 3:

			display_single_Class(classPointer);

			break;

		case 4: 
			list_all_Classes(classPointer);

			break;

			
		case 5: 
			getGPACalulation(classPointer);

			break;

		case 6:
			delete_all_classes(classPointer);
			cout << "All classes deleted!" << endl;
			break;

		case 7:
			delete_all_classes(classPointer);

			break;

		default:

			cout << "Invalid choice" << endl;

		}



	} while (choice != 7);

}

[doug4]

First of all, there is no need for the typedef in line 24. In C++ you can use the name of a struct (or class) without the keyword.

In C++, struct and class mean the same thing except all members of a struct are public by default, and all members of a class are private by default. Many programmers tend to use struct when creating a data structure like in C, basically a convenient way to pass a set of related data around. When member functions are added, these programmers tend to use the keyword class instead.

Your assignment says to add member functions to your class. Member functions operate on the data within the class. That way the data and the functions that operate on the data are bound together in the class definition.

In order to better understand classes, see the following tutorial page from elsewhere on this web site: http://www.cplusplus.com/doc/tutorial/classes/

By the way, your instructions say this:

The destructor ensures that each and every object created will be freed.

The way you have your class defined, you have not defined any member objects that need to be specifically freed. Possibly the title field was meant to be dynamically allocated for this exercise: char* title;. The way you have it defined does not show this, and there is nothing currently in your class that could benefit from a destructor. You might want to check with your teacher to see what he wants.