Array Expander Function Using Pointers

[blairtch]

Still working on this same problem. My assignment is to create a function that accepts an array as an argument and creates an array that is twice the size.

The full problem: "Write a function that accepts an int array and the array ’s size as arguments . The function should create a new array that is twice the size of the argument 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 should return a pointer to the new array . Demonstrate the function by using it in a main program that reads an integer N (that is not more than 50) from standard input and then reads N integers from a file named data into an array ."

I've been trying to get this to work for a few days now. I am completely stuck, hopeless, lost. I don't know what is wrong. One error I keep seeing is invalid conversion from int* to int.

Any help would be appreciated. Thank you!

#include <iostream>
#include <fstream>
using namespace std;

// Prototypes
void *expand(int[], int);
void showArray(int[], int);

int main()
{
const int SIZE = 50;
int values[SIZE] = {1, 2, 3, 4, 5};
int *arrayPtr = 0;		// To point to an array
int n;

cin >> n;
if (n<0 || n>=SIZE)
return 0;

ifstream file;
file.open("data.txt");

// Allocate an array to hold the test scores.
arrayPtr = new int[n];

showArray(values, n);
expand(arrayPtr, n);

file.close();

return 0;
}

void expand(int* arr[], int size)
{
int *copy = new int[size*2];


for (int index = 0; index < size; index++)
    {
    copy[index] = arr[index];
    }


for (int index = size; index < size * 2; index++)
    {
    copy[index] = 0;
    }

return copy;
}


void showArray(int values[], int size)
{

    int *nums = values;

    cout << "The elements of the array are: \n";
    cout << *nums << " ";

    while (nums < &values[size - 1])
    {
        nums++;
        cout << *nums << " ";
    }

}

[shadowCODE]

hope this helps

#include <iostream>
#include <ctime>
#include <cstdlib>
using namespace std;

int* expand(int[], int );

int main()
{
    int n;
    cout<<"Enter array size: ";
    cin>>n;

    srand(static_cast<unsigned>(time(NULL)));

    int randomArray[n];
    int *expanded = new int[n*2];

    for(int i = 0; i < n; i++)  //fill randomArray
        randomArray[i] = rand()%20;

    expanded = expand(randomArray,n);       //expand array

    cout<<"Original array\n";
    for(int i = 0; i < n; i++)
        cout<<randomArray[i]<<" ";
        
    cout<<endl<<endl;
    cout<<"Expanded array\n";
    for(int i = 0; i < n*2; i++)
        cout<<expanded[i]<<" ";
    cout<<endl;
    system("pause");
    return 0;
}
int *expand(int a[], int n)
{
    int *temp = new int[n*2];
    //new fill the array with 0.
    for(int i = 0; i < n; i++)
        temp[i] = a[i];
    return temp;
}

[shadowCODE]

About your updated question,

//read the first N numbers from a file

#include <fstream>
using namspace std;

ifstream input("data.txt");

int N;
cout<<"Enter size: ";
cin>>N;

if(N < 0 || N > 50)
{
    cout<<"Invalid number"<<endl;
    return -1;  //not successful
}

int array[N];

int count = 0;
while(count <= N)
{ 
    input>>array[count];
    count++;
}

Now, continue to expand the array as in the code above.

[blairtch]

You are a lifesaver. Thanks so much I was really struggling with this one.

Here is the final code

#include <iostream>
#include <fstream>
using namespace std;

//Prototype
int* expand(int[], int );

int main()
{

    int n;
    cout<<"Enter array size to generate a random array: ";
    cin>>n;

    if (n < 0 || n > 50)
    {
        cout << "Invalid number." << endl;
        return 0;
    }

    int array[n];

    int count = 0;
    while(count <= n)
    {
        n >> array[count];
        count++;
    }

    ifstream file;
    file.open("data.txt");

int *originalArray = new int[n];
int *expandedArray = new int[n*2];

 expandedArray = expand(originalArray,n);   

    cout<<"Original array\n";
    for(int i = 0; i < n; i++)
        cout<<originalArray[i]<<" ";

    cout<<endl<<endl;
    cout<<"Expanded array\n";
    for(int i = 0; i < n*2; i++)
    cout<<expandedArray[i]<<" ";
    cout<<endl;
    //system("PAUSE");

    file.close();

    delete [] originalArray;
    originalArray = 0;
    delete [] expandedArray;
    expandedArray = 0;
    return 0;

}

// This function expands the array by doubling the array size.
int *expand(int arr[], int n)
{
    int *temp = new int[n*2];
    for(int i = 0; i < n; i++)
        temp[i] = arr[i];
    return temp;
}

[shadowCODE]

No. You got it all mixed up.
Follow this keenly.

#include <iostream>
#include <cstdlib>
#include <fstream>      //input file
using namespace std;

int* expand(int[], int );

int main()
{

    ifstream input("data.txt");     //input file
    int N;

    cout<<"Enter size: ";
    cin>>N;

    if(N < 0 || N > 50)
    {
        cout<<"Invalid number"<<endl;
        return -1;  //not successful
    }

    int array[N];   //original array
    int *expanded = new int[N*2];       //new expanded array
    int count = 0;

    while(count <= N)
    {
        input>>array[count];    //read input to array
        count++;
    }

    expanded = expand(array,N);       //expand array

    cout<<"Original array\n";   //print original array
    for(int i = 0; i < N; i++)
        cout<<array[i]<<" ";

    cout<<endl<<endl;
    cout<<"Expanded array\n";   //print expanded array
    for(int i = 0; i < N*2; i++)
        cout<<expanded[i]<<" ";
    cout<<endl;

    system("pause");
    return 0;
}
int *expand(int a[], int n)
{
    int *temp = new int[n*2]; //create temporary array

    for(int i = 0; i < n*2; i++)    //fill array with 0
        temp[i] = 0;

    for(int i = 0; i < n; i++)  //copy old array to new array
        temp[i] = a[i];

    return temp; //return new array
}

[blairtch]

This works even better, thanks again!

Don't I have to delete the pointers to the array and initialize them to zero?