An array is a consecutive group of memory locations that all have the same name and the same type. To refer to a particular location or element in the array, we specify the array name and the array element position number. The Individual elements of an array are identified using an index. Arrays have upper and lower bounds and the elements have to lie within those bounds. Each index number in an array is allocated individual memory space and therefore users must evade declaring arrays of larger size than required. We can declare an array of any of the basic data types including variant, user-defined types and object variables. The individual elements of an array are all of the same data type.
Arrays occupy space in memory. The programmer specifies the array type and the number of elements required by the array so that the compiler may reserve the appropriate amount of memory. Arrays may be declared as Public (in a code module), module or local. Module arrays are declared in the general declarations using keyword Dim or Private. Local arrays are declared in a procedure using Dim or Static. Array must be declared explicitly with keyword "As".
There are two types of arrays in Visual Basic namely:
Fixed-size array : The size of array always remains the same-size doesn't change during the program execution.
Dynamic array : The size of the array can be changed at the run time- size changes during the program execution.
When an upper bound is specified in the declaration, a Fixed-array is created. The upper limit should always be within the range of long data type.
Declaring a fixed-array
Dim numbers(5) As Integer
In the above illustration, numbers is the name of the array, and the number 6 included in the parentheses is the upper limit of the array. The above declaration creates an array with 6 elements, with index numbers running from 0 to 5.
If we want to specify the lower limit, then the parentheses should include both the lower and upper limit along with the To keyword. An example for this is given below.
Dim numbers (1 To 6 ) As Integer
In the above statement, an array of 10 elements is declared but with indexes running from 1 to 6.
A public array can be declared using the keyword Public instead of Dim as shown below.
Public numbers(5) As IntegerMultidimensional Arrays
Arrays can have multiple dimensions. A common use of multidimensional arrays is to represent tables of values consisting of information arranged in rows and columns. To identify a particular table element, we must specify two indexes: The first (by convention) identifies the element's row and the second (by convention) identifies the element's column.
Static and dynamic arrays
Basically, you can create either static or dynamic arrays. Static arrays must include a fixed number of items, and this number must be known at compile time so that the compiler can set aside the necessary amount of memory. You create a static array using a Dim statement with a constant argument:' This is a static array.
Dim Names(100) As String
Visual Basic starts indexing the array with 0. Therefore, the preceding array actually holds 101 items.
Most programs don't use static arrays because programmers rarely know at compile time how many items you need and also because static arrays can't be resized during execution. Both these issues are solved by dynamic arrays. You declare and create dynamic arrays in two distinct steps. In general, you declare the array to account for its visibility (for example, at the beginning of a module if you want to make it visible by all the procedures of the module) using a Dim command with an empty pair of brackets.
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