Pointers and arrays

[allQuestions]

Can someone explain the reason for pointers. i have setup an array like the following.

int* a = NULL;
int n;
cin >> n;
a = new int[n];

This will setup my array size based on the number that a person enters. If I want to load this array with numbers or if the array was a character array, what will pointers do for me?

[helios]

'a' is a pointer.

[Thumper]

'a' is in fact a pointer, thank you for pointing that out, helios.

Declaring an int *a is essentially the same thing as declaring an array of integers. read http://cplusplus.com/doc/tutorial/pointers/ for more information on pointers.

The reason you need a pointer in this situation is because if you did this

int x;
cin >> x;
int a[x];

you would get a compiler error.

after what you've done already, you can use your array like

a[0] = 20;
a[1] = 5;

cout << a[0] << endl; // etc.  

[Disch]

Declaring an int *a is essentially the same thing as declaring an array of integers

Ehhhhhh

[Thumper]

It's not exactly the same thing... But somewhat the same. Rather, the functionality can be the same.

[allQuestions]

What is the difference then between allocating an array as:
nt* a = NULL;
int n;
cin >> n;
a = new int[n];

and allocating an array as int a[20];

[allQuestions]

so if I use pointer in assigning the array and I have a user input 25 different numbers into the array, will the array hold the address of those numbers or the actual numbers?

[Disch]

What is the difference then between ...

int a[20]; Gives you an array of exactly 20 ints. No more, no less.

int a* = new int[n]; Gives you an array of 'n' ints. This is useful if the value of 'n' is not known at compile time (like if you get it from a file, or from the user)

so if I use pointer in assigning the array and I have a user input 25 different numbers into the array, will the array hold the address of those numbers or the actual numbers?

it will hold the actual numbers.