/* This program demonstrates the use of dynamic memory allocation. 
 * It also shows how to dynamically allocate and use a 2 dimensional array of strings.
 */
#include<iostream>
#include<cstring>

using namespace std;

/* We can pass arrays into functions and receive them as pointers. 
 * When we do this, we can either use the usual array notation with [] or just dereference the pointers.
 * If we do use pointers, we should also increment the pointers to have them move on to the next element.
 * This function swaps the contents of two equal sized integer arrays.
 */
void swap(int *a, int *b, int size)
{
	int temp;
	for(int i=0; i< size; i++)
	{
		temp = *a;
		*a = *b;
		*b = temp;
		a++;
		b++;	
	}
}

/* This function gets an array as a parameter and returns another array, where each element is the element of the old array multiplied by 5.
 * We cannot return whole arrays, but we can return pointers to arrays, and that's the same thing.
 * If the array was created in compile time (without new), this would cause issues if we try to dereference in main
 * Retruning a dynamically allocated array ensures that we have access to data outside the function as well.
 */
int * multiply (int *arr, int size)
{
	int *b = new int[size]; // the new operator is used to dynamically allocate the new array.
	for(int i=0; i< size; i++)
		b[i] = arr[i] * 5;
	return b;
}



int main()
{
	int count, max;
	cout<<"Enter the number of names: ";
	cin>>count;
	cout<<"Enter the size of each string: ";
	cin>>max;

	int arr[] = {5,12,15,-9}; // array fo  integeres

	int *newarr = multiply(arr, 4); // The new array is returned here. We still have access to it.

	cout<<"The new array is: "<<endl;
	for(int i=0; i<4; i++)
		cout<<newarr[i]<<"\t";

	cout<<endl;

	swap(arr, newarr, 4); 

	cout<<"The new array after swap is: "<<endl;
	for(int i=0; i<4; i++)
		cout<<newarr[i]<<"\t";

	cout<<endl;

	//create an array of character pointers.
	// Each of these pointers will point to a Cstring
	char ** list = new char*[count];
	char st[10];
	cin.getline(st,10); //to get rid of trailing newline
	cout<<"Enter the names: ";
	for(int i=0; i<count; i++)
	{
		//create each individual string
		list[i] = new char[max];
		cin.getline(list[i],max, '\n');
	}
	
	cout<<"\nThe names are: "<<endl;
	for(int i=0; i<count; i++)
		cout<<list[i]<<endl;

	int newcount;
	cout<<"\nEnter the new size: ";
	cin>>newcount;
	cin.getline(st,10);//to get rid of trailing newline
	char ** newlist	= new char*[newcount];
	cout<<"Enter the extra names: ";
	for(int i=0; i<newcount; i++)
	{
		
		if(i<count) // If it is old data, we just have the new pointer point to the old string
		{
			newlist[i] = list[i];
		}
		else //If it is new data, we make a new string and read in the value
		{	newlist[i] = new char[max];
			cin.getline(newlist[i],max, '\n');
		}
	}

	//We might have code elsewhere that refers to the list with old names, so we update them here
	list = newlist;
	count = newcount;

	//This just displays the list again
	cout<<"\nThe updated list of names is: "<<endl;
	for(int i=0; i<count; i++)
		cout<<list[i]<<endl;

	//We have to delete the space we created dynamically. Or we'll have dangling references.
	//If we created the data in 2 steps, we should also delete the data in two steps.
	for(int i=0; i<count; i++)
		delete list[i];
	delete list;
	return 0;
}