Pointers (new and delete)

Hi, i've just been working through the pointers chapter in my C++ book and come across a confusing part.

What's the difference between using:

int iAge = 20;
int * pAge = &iAge;

and

int * pAge = new int;
*pAge = 20;

i.e. Why use new and delete when you can just make a pointer like the first method?

Quote:

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Originally posted by Russ
Hi, i've just been working through the pointers chapter in my C++ book and come across a confusing part.

What's the difference between using:

int iAge = 20;
int * pAge = &iAge;

and

int * pAge = new int;
*pAge = 20;

i.e. Why use new and delete when you can just make a pointer like the first method?

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With the first method, your creating a variable on the stack.....this only has a fixed amount of memory.....so say at runtime you needed an amount of ints, but you didnt know how many, youd be stumped as you would be stuck to 1 int.....with the second method you can have as many ints as you choose

int * pAge = new int(20);

See, when u use the following

int iAge = 20;
int * pAge = &iAge;

u r first creating a variable named iage. As pointers can store memory addresses so the pointer pAge is storing the memory address of the iAge.

Now in the latter

int * pAge = new int;
*pAge = 20;
Here,
U r creating a new memory location that will be pointed by pAge.

In the first case,
If u change the valueof iAge to 30 then u 'll find that
the value of *pAge also becomes 30.

In the latter case,
The value of *pAge can be changed only by :
*pAge=30;

Consult a book 4 betterment of concepts.