Lesson 9 : Looping - Visual Basic Tutorial

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VB6 Home 1. Intro to VB6 2. App Development 3. Using Controls 4. Code Writing 5. VB Data Types 6. Variables 7. If & IIf Statements 8. Select Case 9. Looping Structures 10. Functions Overview 11. Math Functions 12. Formatting Functions 13. String Functions 14. Sub Procedures 15. Excel VBA Functions 16. Arrays 17. File Creation 18. Graphics Creation 19. DVD Player App 20. Audio Player App 21. Picture Viewer 22. Multimedia Player 23. Database Basics 24. Advanced Database 25. Using ADO Control 26. DataGrid Control 27. SQL Queries 28. Advanced SQL 29. E-library App 30. Animation Part 1 31. Animation Part 2 32. Animation Part 3 33. Web Browser App 34. FTP Program 35. Errors Handling 36. Complie & Distribute 37. Menu Creation 38. Keyboard Handling 39. Printing 40. Final Lesson

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Key Takeaway

Loops are fundamental programming structures that enable efficient repetition of code blocks. Mastering loops is essential for automating repetitive tasks and creating efficient VB6 applications.

Welcome to Lesson 9 of our Visual Basic 6 Tutorial! In this lesson, you'll master VB6's powerful looping structures that allow you to efficiently repeat blocks of code. Loops are essential for automating repetitive tasks, processing collections of data, and creating dynamic applications.

9.1 Introduction to Loops

Loops are programming constructs that enable the execution of code blocks repeatedly until specific conditions are met. VB6 offers three primary loop structures:

Do Loops

Most flexible looping structure with condition checking at start or end

For...Next Loops

Ideal for iterating a specific number of times

While...Wend Loops

Simple looping while condition remains true

Figure 9.1: Loop Execution Flow

Visual representation of loop execution flow

How Loops Work

Loops repeatedly execute a block of code as long as a specified condition remains true. The condition is evaluated before each iteration (in pre-test loops) or after each iteration (in post-test loops). Proper loop termination is crucial to avoid infinite loops.

Initialization

Set starting values before entering the loop

Condition Check

Evaluate whether to continue looping

Iteration

Execute loop body and update control variable

9.2 The Do Loop

The Do Loop is the most flexible looping structure in VB6, with four syntax variations:

1 Pre-test While Loop

Do While condition ' Code to execute Loop

Checks condition before each iteration

2 Post-test While Loop

Do ' Code to execute Loop While condition

Checks condition after each iteration

3 Pre-test Until Loop

Do Until condition ' Code to execute Loop

Runs until condition becomes true

4 Post-test Until Loop

Do ' Code to execute Loop Until condition

Runs at least once before checking condition

Important Note

Pre-test loops may not execute at all if the initial condition is false, while post-test loops always execute at least once.

Example 9.1: Counting with Do Loop

Counter.vb Private Sub CountNumbers_Click() Dim counter As Integer counter = 1 Do While counter