Array

Imagine that you have been given the following programming task:

Read an integer N , which will be at the most 25, then read a list of N numbers and print the numbers out in reverse order.

To solve the problem we need to set up an array that has n entries..

In C
main()
{
#define nums 25
int arr[nums],i;
.. code here ..
}

An array is a predetermined number of storage locations set aside to store a predetermined number of data items, the size is fixed at program compilation time.

Data can be stored and accessed by means of index values which keep track of the serial location of each data entry.

Data can be stored using:

Random organisation - random order
Serial organisation - sorted by key
Usage frequency - most used first
Positioned - based on a numerical sequence of keys

May be:

1 dimensional: 1 to 1 relationship between an entry and its index

In C (and Pascal) we define a string as an array of characters
(here msg[3] = "l")

main()
{
char msg[30];
strcpy (msg,"Hello, world\n");
puts(msg);
}

An array of one dimension with 4 entries in sequence by key

in Pascal:

type
client = record
            key: integer;
            LastName,FirstName: string[30];
          end;
var
Clients : array[1..100] of client;

Multi-dimensional: 1 to many relationship between an entry and its index

In Pascal we could store integers in an 8 x 8 grid using
var checkerboard: array [1..8, 1..8] of Integer;

A two dimension array with 4 records (rows) and 5 fields (columns)

in Pascal:

type
grades = record
            key: integer;
            grade: array[1..4] of integer;
          end;
var
Clients : array[1..100] of client;

So Clients[2].grade[1] = 70.

dadsar03.gif (3248 bytes)

Another multidimensional array structure we are familiar with is the Windows menu system.

w98cp.gif (23802 bytes)

So the "by Date" option could be
Menu(3,10,4).

dba97_01.gif (45645 bytes)

MS-Access allows us to easily add or modify the menus as shown left;