Question

I’m doing a lot of different things with manipulating arrays without vectors, I was wondering if any one could help me with shifting elements in an array and expanding an array while initializing the new space with elements. I feel like I’m very close to completing this code, but I’m hitting a block.

#include <iostream>
using namespace std;


// Function prototypes
int *reverse(int *, int);
int *expand(int *, int); 
int *shift(int *, int); 
void display(int[], int);
void display2(int[], int);
void display3(int[], int);


int main()
{
    int const SIZE = 5;
    int myArray [SIZE] = {1, 2, 3, 4, 5};
    int myArray2 [SIZE] = {1, 2, 3, 4, 5};
    int myArray3 [SIZE] = {1, 2, 3, 4, 5};

    int *arraPtr;
    int *arraPtr2;
    int *arraPtr3;

    arraPtr = reverse(myArray, SIZE);

    display(myArray, SIZE);

    arraPtr2 = expand(myArray2, SIZE);

    display2(myArray2, SIZE);

    arraPtr3 = shift(myArray3, SIZE);

    display3(myArray3, SIZE);

    delete [] arraPtr;
    delete [] arraPtr2;
    delete [] arraPtr3;


    return 0;
}



int *reverse(int *arr, int size)
{
    int *copyArray;
    int posChange;

    if( size < 0)
        return NULL;

    copyArray = new int[size];

    for (int index = 0; index < --size; index++)
    {
            posChange = arr[index];
            arr[index] = arr[size];
            arr[size] = posChange;

    }
    return copyArray;

}


int *expand(int *arr, int size)
{
    int *newArray;

        newArray = new int[size * 2];
memcpy( newArray, arr, size * sizeof(int));
for (int index = size; index < (size*2); index++)
    newArray[index] = 0;
return newArray;




}

int *shift(int *arr, int size)
{
    int *newArray;
    newArray = arr;
    newArray = new int [size + 1];
    for (int index = 5; index > 0; index--)
        newArray[index] = newArray[index - 1];

return newArray;


}

void display(int arr[], int size)
{
    for (int index = 0; index < size; index++)
    {
        cout << arr[index] << " ";
    }

        cout << endl;
}

void display2(int arr[], int size)
{
    for (int index = 0; index < size; index++)
    {
        cout << arr[index] << "  ";
    }
        cout << endl;

}

void display3(int arr[], int size)
{
    for (int index = 0; index < size; index++)
    {
        cout <<arr[index] << "  ";
    }
        cout << endl;

}

Answer 1

There are only two compile error: int newArray; should be int* newArray; and #include <cstring> is missing (necessary for memcpy())

Also, the line display(myArray, SIZE); was probably meant to be display(arraPtr, SIZE); and likewise display2(myArray2, SIZE); — otherwise you’re only displaying the original arrays, not the results of your function calls.

However, this could benefit from the safer and more generic C++ algorithms, std::copy() and std::reverse_copy() at least:

int *reverse(int *arr, int size)
{
    int *copyArray = new int[size];
    std::reverse_copy(arr, arr+size, copyArray);
    return copyArray;
}
int *expand(int *arr, int size)
{
    int *newArray = new int[size * 2]();
    std::copy(arr, arr+size, newArray);
    return newArray;
}
int *shift(int *arr, int size)
{
    int* newArray = new int [size + 1]();
    std::copy(arr, arr+size, newArray+1);
    return newArray;
}

full program: https://ideone.com/RNFiV