c++ what is "pointer = new type" as opposed to "pointer = new type []"?

Question

In many tutorials, the first code samples about dynamic memory start along the lines of:

int * pointer;
pointer = new int;        // version 1
//OR
pointer = new int [20];    // version 2

They always proceed to explain how the second version works, but totally avoid talking about the first version.

What I want to know is, what does pointer = new int create? What can I do with it? What does it mean? Every tutorial without fail will avoid talking about the first version entirely. All I've found out (through messing about) is this:

#include <iostream>

using namespace std;

int main()
{
    int * pointer;
    pointer = new int;
   pointer[2] = 1932;   // pointer [2] exists? and i can  assign to it?!
   cout << pointer[2] << endl;      // ... and access it successfully?!
};

The fact that I can subscript pointer tells me so far that pointer = new int implicitly creates an array. But if so, then what size is it?

If someone could help clear this all up for me, I'd be grateful...

Answer 1

My teacher explained it like this.
Think of cinema. The actual seats are memory allocations and the ticket you get are the pointers.

int * pointer = new int;

This would be a cinema with one seat, and pointer would be the ticket to that seat

pointer = new int [20] 

This would be a cinema with 20 seats and pointer would be the ticket to the first seat. pointer[1] would be the ticket to the second seat and pointer[19] would be the ticket to the last seat.

When you do int* pointer = new int; and then access pointer[2] you're letting someone sit in the aisle, meaning undefined behaviour