Why can't I reuse the name of a dynamically-allocated array after I delete it in C++?

Question

So, I was giving some examples of how to use dynamically-allocated 2d arrays and was about to send code that was essentially the following:

int size = 5;
int* arr = new int[ size ];
for( int i = 0; i < size; i++ )
    arr[ i ] = i;
delete[] arr;

size = 10;
int* arr = new int[ size ];
for( int i = size; i > 0; i-- )
    arr[ i ] = i;
delete[] arr;

This gave me a redefinition error, but I thought that delete[] frees the space in memory (and thus 'arr'). I know how to work around this (new array name, don't delete[]/redefine), but I was wondering what's actually going on that gives the error?

Answer 1

You might want to try this:

int size = 5;
int* arr = new int[ size ];
for( int i = 0; i < size; i++ )
    arr[ i ] = i;
delete[] arr;

size = 10;
arr = new int[ size ]; //<-- no int* here, we just need to reassign
for( int i = size; i > 0; i-- )
    arr[ i ] = i;
delete[] arr;

We are indeed deallocating the block of memory arr points to, but that doesn't mean we are removing the int* arr. We just removed it's 'content'.

It's just a non assigned pointer again after we delete it.

Answer 2

The arr is declared twice. You can reuse it but without declare it again.

size = 10;
int* arr = new int[ size ];