Lesson 16 : Arrays - Visual Basic Tutorial

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Key Takeaway

Arrays in VB6 allow you to efficiently store and manipulate collections of related data using a single variable name and index numbers.

Welcome to Lesson 16 of our Visual Basic 6 Tutorial! In this lesson, you'll master VB6's powerful array features that allow you to efficiently manage collections of related data. Arrays are essential for handling lists of items, tables of information, and any situation where you need to work with multiple values of the same type.

16.1 Introduction to Arrays

An array is a powerful tool in programming, allowing us to represent multiple items with a single variable. Instead of dealing with individual items, we can use an array to handle a list of similar items efficiently.

Without Arrays

• Declaring 100 separate variables for 100 names
• Complex code with excessive If...Then statements
• Time-consuming and inefficient
• Hard to maintain and scale

With Arrays

• Single array variable for all names
• Access items via index (name(1), name(2), etc.)
• Simplified code using loops
• Easier to maintain and scale

Consider the scenario where we need to enter one hundred names. It would be impractical and time-consuming to declare 100 different variables for each name. Moreover, if we intend to process this data and make decisions based on it, we would end up with an excessive number of if...then statements, leading to a waste of time and effort.

16.2 Dimensions of an Array

Arrays in VB6 can have one or more dimensions, allowing you to represent various data structures:

One-Dimensional Arrays

Like a list of items or a table that consists of one row or one column of items.

Dim ArrayName(x) As DataType Name(0) Index 0 Name(1) Index 1 Name(2) Index 2 Name(3) Index 3

Two-Dimensional Arrays

A table of items that make up rows and columns.

Dim ArrayName(x,y) As DataType

Year	7	8	9
Football	StuGames(1,7)	StuGames(1,8)	StuGames(1,9)
Basketball	StuGames(2,7)	StuGames(2,8)	StuGames(2,9)

16.3 Declaring Arrays

We can use Public or Dim statement to declare an array just as the way we declare a single variable. The Public statement declares an array that can be used throughout an application while the Dim statement declares an array that could be used only in a local procedure.

16.3.1 Declaring One-Dimensional Arrays

The general syntax to declare a one-dimensional array:

Dim arrayName(subscript) As dataType

Where subscript indicates the last index in the array. Note that by default, arrays in VB6 start at index 0.

ArrayDeclaration.vb ' Declare an array with 11 elements (indexes 0 to 10) Dim CusName(10) As String ' Use Option Base 1 to start arrays at index 1 Option Base 1 Dim CusName(10) As String ' 10 elements (1 to 10) ' Specify explicit bounds Dim Count(100 To 500) As Integer

Example 16.3: Student Names

This program accepts student names through an input box and displays them in a list box.

StudentNames.vb Dim studentName(1 To 10) As String Dim num As Integer Private Sub addName() For num = 1 To 10 studentName(num) = InputBox("Enter the student name") If studentName(num) <> "" Then List1.AddItem studentName(num) Else End End If Next End Sub Private Sub Start_Click() addName End Sub

Figure 16.1: Student names interface

16.3.2 Declaring Two-Dimensional Arrays

Two-dimensional arrays are perfect for representing tabular data with rows and columns.

Dim ArrayName(Sub1, Sub2) As dataType

Example 16.5: Student Games

This example tracks student participation in games across different year levels.

StudentGames.vb ' 4 games, 6 year levels (7 to 12) Dim StuGames(1 To 4, 7 To 12) As Integer

Year	7	8	9	10	11	12
Football	StuGames(1,7)	StuGames(1,8)	StuGames(1,9)	StuGames(1,10)	StuGames(1,11)	StuGames(1,12)
Basketball	StuGames(2,7)	StuGames(2,8)	StuGames(2,9)	StuGames(2,10)	StuGames(2,11)	StuGames(2,12)
Tennis	StuGames(3,7)	StuGames(3,8)	StuGames(3,9)	StuGames(3,10)	StuGames(3,11)	StuGames(3,12)
Hockey	StuGames(4,7)	StuGames(4,8)	StuGames(4,9)	StuGames(4,10)	StuGames(4,11)	StuGames(4,12)

Example 16.6: Sales Volume

This program summarizes sales volume for four products over six months.

SalesVolume.vb Private Sub cmdAdd_Click() Dim prod, mth As Integer ' prod is product and mth is month Dim saleVol(1 To 4, 1 To 6) As Integer Const j = 1 listVolume.AddItem vbTab & "January" & vbTab & "February" & vbTab & "March" _ & vbTab & "Apr" & vbTab & "May" & vbTab & "June" listVolume.AddItem vbTab & "____________________________________________" For prod = 1 To 4 For mth = 1 To 6 saleVol(prod, mth) = InputBox("Enter the sale volume for product " & prod & " month " & mth) Next mth Next prod For i = 1 To 4 listVolume.AddItem "Product" & i & vbTab & saleVol(i, j) & vbTab & saleVol(i, j + 1) & vbTab _ & saleVol(i, j + 2) & vbTab & saleVol(i, j + 3) & vbTab & saleVol(i, j + 4) & vbTab & saleVol(i, j + 5) Next i End Sub

Figure 16.2: Sales volume output

16.4 Dynamic Arrays

Dynamic arrays allow you to resize arrays during runtime when the number of elements is unknown at design time.

Static Arrays

• Fixed size determined at design time
• Size cannot be changed at runtime
• Simple but inflexible
• Syntax: Dim arr(10) As Integer

Dynamic Arrays

• Size can be set/reset at runtime
• Flexible for varying data sizes
• Use ReDim to resize
• Syntax: Dim arr() As Integer

Example 16.7: Dynamic Squares

This program demonstrates dynamic arrays by calculating squares of numbers.

DynamicSquares.vb Private Sub cmd_display_Click() Dim myArray() As Integer Dim i, n As Integer n = InputBox("Enter the upper bound of array") List1.Clear ReDim myArray(n) ' Resize the array For i = 1 To n myArray(i) = i ^ 2 List1.AddItem myArray(i) Next End Sub Simulate Dynamic Array

Dynamic Array Output:

Lesson Summary

In this lesson, you've mastered VB6's essential array techniques:

Array Fundamentals

Understanding what arrays are and why they're useful

Dimensions

Working with one-dimensional and multi-dimensional arrays

Declaration

Properly declaring arrays with explicit bounds

Dynamic Arrays

Creating flexible arrays that resize at runtime

Best Practice

Use dynamic arrays with the ReDim Preserve statement when you need to preserve existing values while resizing. Remember that ReDim alone will erase existing values in the array.

Practice Exercises

Test your understanding of VB6 arrays with these exercises:

Exercise 1: Temperature Records

Create an array to store daily temperatures for a month and calculate the average.

Exercise 2: Student Grades

Use a two-dimensional array to store student grades for multiple subjects.

Exercise 3: Dynamic Inventory

Create a program that allows users to add items to a dynamic array.

Exercise 4: Array Sorting

Implement a bubble sort algorithm to sort an array of numbers.

Exercise 5: Matrix Operations

Create functions to add and multiply two-dimensional arrays (matrices).

Next Lesson

Continue your VB6 journey with Lesson 17: Creating Files in VB6.

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