Im trying to Increase and Decrease the size of an array

[TarikNeaj]

Im trying to do my homeworks and its basically this. First I try to double the size of my array (from 5 to 10) then I try to decrease the size of it by Only one element.

This is what Ive done.

  int size = 5;
int theKingOfKeepingSizes = size;
string *arr = new string[size];

size = size + 5;

string *arr2 = new string[size];


for (int i = 0; i < theKingOfKeepingSizes; i++)
{
    arr2[i] = arr[i];
}

delete[] arr;

arr = arr2;

int newsize = size - 1;
string *arr3 = new string[newsize];

for (int i = 0; i < newsize; i++)
{
    arr3[i] = arr2[i];
}

delete[] arr2;

arr2 = arr3;

Before you tell me "vector" can be used, I know. Im just following instructions. Am I doing it right though? If Im not, what can I improve, and. If Im doing it right, how can I put it to test? with names maybe? Im unsure on how to do that.

Thank you!

[ne555]

you invalidated `arr' at line 27.
the client should only have to worry about calling your expand and shrink functions, and not having to follow all those temporaries.

[dhayden]

Expanding on what ne555 said, it would be cleaner if your wrote a function to resize your array:

// Given an array arr with size elements, resize it
// to contain newSize elements. This creates a new array with newSize elements
// and copies the appropriate number of elements from arr to it. The original
// array is deleted and then arr and size are modified to contain the
// new values
string *resize(string * &arr, int &size, int newSize);

Once you have this, your code becomes

string *arr = new string[size];
resize(arr, size, 10);
resize(arr, size, size-1);