New to programming and having issues expanding an array to display zeroes - c++

Question

I am having some issues with an array expansion project and am trying to find where the issue is with getting my array to expand with all zeroes. Here are the requirements:
Array Expander. The program should have an array of integers. It will have a function that has two parameters, the integer array and the array’s size. This function will create a new array that is twice the size of the arguments array. The function should copy the contents of the argument array to the new array, and initialize the unused elements of the second array with 0. The function must return a pointer to the new array. The program will then display the contents of the new array.
Program must have the following functions
• int* expandArray(int[ ], int)
• void showArray(int [ ], int)
I am getting the program to build the first array without issues, however, the second array, while it displays the first array of numbers fine, displays the second array with an assortment of digits. I have been looking at this for hours and am at a loss with how to correct this to work correctly. Here is my code that I have so far:
//Include section
#include <iostream>
#include <cstring>
//Namespace Section
using namespace std;
//Function Prototype Section
int *expandArray(int[], int&);
void showArray(const int[], int);
//Main section: this is the entry point of the program, which controls the flow of execution
int main()
{
int arraySize = 7; //sets the size of the array at 7
int *array = new int[arraySize];
for (int c = 0; c < arraySize; ++c)
array[c] = c + 1;
//the following outputs the initial array of 7 to the user's screen; beginning at 1 and incrementing to 7
cout << "*********************************************************************" << endl;
cout << " The following is the initial array " << endl;
cout << "*********************************************************************" << endl;
cout << endl;
showArray(array, arraySize);
cout << endl;
cout << endl;
//the following outputs the initial array, plus expands the array by double, initializing the unused elements with zero
cout << "*********************************************************************" << endl;
cout << " The following is the expanded array " << endl;
cout << "*********************************************************************" << endl;
cout << endl;
showArray(array, arraySize * 2);
cout << endl;
cout << endl;
delete[] array;
system("PAUSE");
return 0;
}
int *expandArray(int array[], int &arraySize)
{
int *expandedArray;
expandedArray = new int[arraySize * 2];
for (int index = arraySize; index < (arraySize * 2); index++)
expandedArray[index] = 0;
arraySize *= 2;
delete[] array;
return expandedArray;
}
void showArray(const int arr[], int arraySize)
{
for (int index = 0; index < arraySize; index++)
cout << arr[index] << " " << endl;
}
I believe my issue is in the following section of the code, but unsure as to how to fix it:
int *expandArray(int array[], int &arraySize)
{
int *expandedArray;
expandedArray = new int[arraySize * 2];
for (int index = arraySize; index < (arraySize * 2); index++)
expandedArray[index] = 0;
arraySize *= 2;
delete[] array;
return expandedArray;
Any assistance would be greatly appreciated!

Answer 1

As I see it you forgot to to copy the contents of your initial array into expandedArray in the declaration of your function. You only set all elements with index in between arraySize and arraySize*2 to 0 but never actually copied the values of your argument.
I would include the following:
for(int i=0; i<arraySize; i++) expandedArray[i] = array[i];
right after having declared expandedArray dynamically. Note it is important that you include this piece of code before modifying arraySize as you would get out-of-bounds issues when accessing array[i].

Answer 2

The issue is that you're not copying the original array's contents into the new allocated array space.
A simple solution is to use new[] with brace initialization of 0, and then copy the original contents into the new array. The brace initialization will initialize all the space to 0, so you don't need to write two loop to set the newly allocated space to 0.
int *expandArray(int array[], int &arraySize)
{
int *expandedArray;
// allocate and initialize all entries to 0
expandedArray = new int[arraySize * 2]{0};
// copy old elements to new space
for (int index = 0; index < arraySize; index++)
expandedArray[index] = array[index];
// delete old space
delete [] array;
// double array size
arraySize *= 2;
return expandedArray;
}

Answer 3

int *arrayExpander(int arr[], int size)
{
int *expendedArray = new int[size * 2];
// move elements forom original array into the expandedArray
// initilize the rest of the elements to ZERO
for (int i = 0; i < size * 2; i++)
{
if (i < size)
{
// filling firt half
expendedArray[i] = arr[i];
}
else
{
// second half of the array
expendedArray[i] = 0;
}
}
return expendedArray;
}
int main()
{
int size = 5;
int arr[] = { 1,2,3,4,5 };
// Array pointer
int *arrPtr = arrayExpander(arr, size);
// Display
for (int i = 0; i < size * 2; i++)
{
cout << arrPtr[i] << " " << flush;
}
return 0;
}

Answer 4

Actually there are 2 errors in your code:
When you run your code it prints the first 7 elements of your array of type double correctly, but not the other 7. This is because they are not initialized, therefore they are returning garbage values.
Therefore in the function you have to initialize the other 7 elements to 0. The same goes for the first 7 elements and the first matrix.
I rectified the problem. Please have a good look at it:
//Include section
#include <iostream>
#include <cstring>
//Namespace Section
using namespace std;
//Function Prototype Section
int *expandArray(int[], int&);
void showArray(const int[], int);
int *expandedArray;
//Main section: this is the entry point of the program, which controls the flow of execution
int main()
{
int arraySize = 7; //sets the size of the array at 7
int *array = new int[arraySize];
for (int c = 0; c < arraySize; ++c)
array[c] = c + 1;
//the following outputs the initial array of 7 to the user's screen; beginning at 1 and incrementing to 7
cout << "*********************************************************************" << endl;
cout << " The following is the initial array " << endl;
cout << "*********************************************************************" << endl;
cout << endl;
showArray(array, arraySize);
cout << endl;
cout << endl;
//the following outputs the initial array, plus expands the array by double, initializing the unused elements with zero
cout << "*********************************************************************" << endl;
cout << " The following is the expanded array " << endl;
cout << "*********************************************************************" << endl;
cout << endl;
expandArray(array, arraySize);
showArray(expandedArray, arraySize);
cout << endl;
cout << endl;
delete[] array;
return 0;
}
int *expandArray(int array[], int &arraySize)
{
expandedArray = new int[arraySize * 2];
for (int c = 0; c < arraySize; ++c)
expandedArray[c] = c + 1;
for (int index = arraySize; index < (arraySize * 2); index++)
expandedArray[index] = 0;
arraySize *= 2;
delete[] array;
return expandedArray;
}
void showArray(const int arr[], int arraySize)
{
for (int index = 0; index < arraySize; index++)
cout << arr[index] << " " << endl;
}
//here is your solution bro..!!