SCRIPTING: Arrays [22910]

Arrays

 

It is often the case that multiple pieces of information need to be used as a single variable. The best way to handle this is through the use of an array. An array is a storage unit for many items of the same type. The storage unit is comprised of multiple items of one type, each being stored in their own index within the array. Think of it as a filing drawer that may contain many files in a specific order which all pertain to a single topic. The array would be the drawer while the individual files within would be the indices.

 

NOTE: These examples are designed to illustrate the syntax of E-Basic array declarations only, and are not intended to be implemented and generated.

 

Declaring Arrays
To work with an array, refer to the name of the array and the index. An array can be of any data type, but can only hold a single data type. Specifically, you can declare an array that holds strings and an array that holds integers, but you cannot declare a single array that holds both strings AND integers. However, if you need to store multiple data types in a single array, you may declare arrays of variant data type, which holds any kind of data. Be careful though; since variant data typically is more memory intensive than other data types, creating and using an arrays of variants can potentially create an overwhelming amount of overhead. Use this option wisely.

 

As with any variable, before using it, first declare and initialize it. The declaration of an array is similar to any other variable. The Dim statement is used, and the only significant difference is that the array declaration also takes a dimensions value.

 

Dim position_array ( ) As Integer

Fixed Arrays
The dimensions of fixed arrays cannot be adjusted at execution time. Once declared, a fixed array will always require the same amount of storage. Fixed arrays can be declared with the Dim statement by supplying explicit dimensions. The following example declares a fixed array of eleven strings (arrays are zero-based) see Using an Array Index below):
 

Dim a(10) As String

 

Fixed arrays can be used as members of user-defined data types. The following example shows a structure containing fixed-length arrays:

 

Type Foo

Rect(4) As Integer

Colors(10) As Integer

End Type

 

Only fixed arrays can appear within structures. Refer to Stage 7, Step 2: User-Defined Data Types (Page 153) for a discussion of user-defined types.

 

Dynamic Arrays
Dynamic arrays are declared without explicit dimensions, as shown below:

 

Public Ages() As Integer

 

Dynamic arrays can be resized at execution time using the ReDim statement:

 

ReDim Ages (100)

 

Dynamic arrays cannot be members of user-defined data types.

 

Using an Array Index
Items within an array are indexed beginning with zero. In other words, the first element within an array is located within index number 0. For instance, if an array is designed to hold 10 elements, the array should be dimensioned as in the following:

 

Dim arrResponses (9) As String

 

In the previous statement, the arrResponses array is dimensioned to hold 10 elements. Because array indices begin at 0, the “9” in the dimension statement indicates the largest legal index within the array, and the total number of elements that the array may contain is one greater than this number.
 
Addressing an Element within an Array
The individual elements within an array accessed or set simply by listing the array name, followed by subscript notation (i.e., the index number enclosed in parentheses) to refer to the appropriate index. The index of the array includes an integer value for each dimension of the array. For example, my _array(3) refers to, or identifies the value in the fourth slot in the array called my _array Data contained within an array may be used like any other variables:

Assign a value to an array element.

 

Dim a(9) As Integer

a(0) = 12

 

Assign a value stored in an array to another variable.

 

x = a(0)

 

Use the value of an array element in an expression:

 

x = 10 * a(0)

Assigning Data to Array Indices
When an array is declared using the Dim statement, the elements composing the array are not initialized. That is, the elements contain no valid information. Before accessing the array elements, they must be assigned meaningful values. Array elements are assigned values using an assignment expression (i.e., ArrayName(Index) = Expression).

 

Dim a(9) As Integer

a(0) = 12

 

The most efficient method of assigning values to an entire array at one time (e.g., to initialize an array to consecutive values) is to use a For…Next loop.

 

ReDim Preserve Ages (100)

 

Dynamic arrays cannot be members of user-defined data types.

 

Using an Array Index
Items within an array are indexed beginning with zero. In other words, the first element within an array is located within index number 0. For instance, if an array is designed to hold 10 elements, the array should be dimensioned as in the following:

'create an array with 1- indices, numbered 0 through 9

Dim a(9) As Integer

Dim x As Integer

Dim i As Integer

For i = Lbound(a) To Ubound(a)

a(i) = x

x = x + 1

Next i

Arrays may also be multi-dimensional. Arrays containing more than one dimension are similar to a spreadsheet-like organization, with different dimensions handling different tables or lists of information. Multi-dimensional arrays are declared just like one-dimensional arrays, with commas separating the values specifying the size of each dimension in the array.

 

Dim multi_array(9,6,8) As Integer

 

The total number of elements held by a multi-dimensional array is equal to the product of the sizes of the individual dimensions. The example above would result in an array holding 630 elements (10 by 7 by 9).