Abstract Classes and Overloading Ouput Operator - c++

Question

Okay this program is to let some user enter an amount of numbers and it will output them in a straight line with commas in between. I have got every other code to work except for overloading the output operator.
Here's the header file:
#ifndef LISTTYPE_H_INCLUDED
#define LISTTYPE_H_INCLUDED
#include <iostream>
class ListType {
public:
ListType(size_t=10);
virtual ~ListType();
virtual bool insert(int)=0;
virtual bool erase();
virtual bool erase(int)=0;
virtual bool find(int) const=0;
size_t size() const;
bool empty() const;
bool full() const;
friend std::ostream& operator << (std::ostream&, const ListType&);
protected:
int *items;
size_t capacity;
size_t count;
};
Here's the cpp file:
#include "ListType.h"
ListType::ListType (size_t a) {
capacity = a;
count = 0;
items = new int [capacity];
}
ListType::~ListType() {
delete [] items;
}
bool ListType::erase() {
count = 0;
return 0;
}
size_t ListType::size() const {
return (count);
}
bool ListType::empty() const {
return (count == 0);
}
bool ListType::full() const {
return (count == capacity);
}
std::ostream& operator << (std::ostream& out, const ListType& list1) {
int a = 0;
out << list1[a] << ", " ;
return out;
}
Any help will be deeply appreciated.

Answer 1

You can use a function similar to this in your class:
void ListType::output(std::ostream& out) const {
for (int i = 0; i < count; i++) {
if (i > 0) { // No comma for first element
out << ", ";
}
out << items[i];
}
}
The overloaded << method of ostream can then be rewritten to this to call the output function:
std::ostream& operator << (std::ostream& out, const ListType& my_list) {
my_list.output(out);
return out;
}