Nrthugu

Im trying to understand pointers but im having trouble increasing the size of an array, what im trying to do is make an array that is one bigger than the standard array, copy over everything there, then delete the old pointer array, create a new pointer array that is the right size and move back everything from this temp array. For some reason I keep getting "Unable to read memory" and I have no clue why.

#include <iostream>



int main()

{

    int number;

    int arraySize = 3;

    bool full;

    int *ptr = new int[arraySize] {0};



do

{

    full = false;

    std::cout << "Input a number please: ";

    std::cin >> number;



    getchar();



    for (int i = 0; i < arraySize; i++)

    {

        if (ptr[i] == 0)

        {

            ptr[i] = number;

            i = arraySize;

        }

        else if(arraySize -1 == i)

        {

            full = true;

        }

    }

    if (full == true)

    {

        int *tempPtr = new int[arraySize+1];

        for (int x = 0; x < arraySize; x++ )

        {

            tempPtr[x] = ptr[x];



        }

        delete ptr;

        arraySize++;

        int *ptr = new int[arraySize];

        for (int x = 0; x < arraySize; x++)

        {

            ptr[x] = tempPtr[x];



        }

        ptr[arraySize] = number;



    }







}while(number != -1);

for (int z = 0; z < arraySize; z++)

{

    std::cout << ptr[z] << std::endl;

}



getchar();

return 0;

}

int *ptr = new int[arraySize];

This will not be the same ptr as the outer ptr so it will leak when it goes out of scope. It should be

ptr = new int[arraySize];

Also, don't forget to delete ptr before you exit the program. Here's a slightly modified version that is easier to read i.m.o.

#include <iostream>



int main()

{

    int number;

    int arraySize = 3;

    int *ptr = new int[arraySize] {0};

    int i=0;



    do

    {

        std::cout << "Input a number please: ";

        std::cin >> number;

        std::cin.ignore();

        if(number==-1) break; // no need to increase array



        if(i>=arraySize) {

            // the array is full

            int *tempPtr = new int[arraySize+1];

            for (int x = 0; x < arraySize; ++x) tempPtr[x] = ptr[x];

            delete ptr;



            // just assign the address tempPtr is pointing at to ptr

            ptr = tempPtr;

            ++arraySize;

        }

        // store the new number  

        ptr[i] = number;

        ++i;

    } while(true);



    for (int z = 0; z < i; z++)

    {

        std::cout << ptr[z] << std::endl;

    }

    delete ptr;



    getchar();

    return 0;

}

Note that there are standard containers (std::vector etc) dealing with dynamic allocation more efficiently than this so you don't have to write it yourself.