Lesson 15: Mastering Loops in VB2022

Implementing efficient repetition with loops in Visual Basic

Key Takeaway

Loops are fundamental programming constructs that allow you to execute code repeatedly. VB2022 offers several loop types optimized for different scenarios, enabling efficient repetition and iteration through collections.

Welcome to Lesson 15 of our Visual Basic 2022 Tutorial! In this lesson, you'll master the art of repetition with loops. You'll learn how to implement different loop structures, choose the right loop for each scenario, and create efficient algorithms that process data iteratively.

Learning Objectives

Understand when to use different loop types
Master For...Next loops for fixed iterations
Implement Do...Loop structures for conditional repetition
Utilize While...End While loops
Control loop execution with Exit statements
Create nested loops for multi-dimensional processing
Apply loops to real-world programming challenges

15.1 Loop Fundamentals

Loops execute a block of code repeatedly until a specified condition is met. Choosing the right loop structure is crucial for efficient and readable code.

Loop Execution Flow

15.1.1 When to Use Each Loop Type

Different loop structures serve different purposes:

Loop Type	Best For	Key Features
For...Next	Fixed number of iterations	Counter variable, Step increment
Do...Loop	Condition-based repetition	Pre-test and post-test variations
While...End While	Condition-first looping	Simple condition check
For Each...Next	Iterating through collections	Automatic element iteration

15.2 For...Next Loop

The For...Next loop executes code a specific number of times. Ideal when you know the exact number of iterations needed.

15.2.1 Basic Syntax

ForNextSyntax.vb

For counter = start To end [Step increment]
    ' Code to execute
Next [counter]

Best Practice

Always include the counter variable in the Next statement to make your code more readable and to avoid nested loop confusion.

15.2.2 Practical Examples

1 Multiplication Table

Generate a multiplication table using a For loop:

MultiplicationTable.vb

Private Sub BtnGenerateTable_Click(sender As Object, e As EventArgs) Handles BtnGenerateTable.Click
    Dim num As Integer = Integer.Parse(txtNumber.Text)
    lstTable.Items.Clear()
    
    For i As Integer = 1 To 10
        lstTable.Items.Add($"{num} x {i} = {num * i}")
    Next
End Sub

2 Sum of Even Numbers

Calculate the sum of even numbers in a range:

SumEvenNumbers.vb

Private Sub BtnCalculateSum_Click(sender As Object, e As EventArgs) Handles BtnCalculateSum.Click
    Dim startNum As Integer = Integer.Parse(txtStart.Text)
    Dim endNum As Integer = Integer.Parse(txtEnd.Text)
    Dim sum As Integer = 0
    
    For i As Integer = startNum To endNum Step 2
        If i Mod 2 = 0 Then
            sum += i
        End If
    Next
    
    lblResult.Text = $"Sum of even numbers: {sum}"
End Sub

3 Pattern Generation

Create patterns using nested For loops:

PatternGeneration.vb

Private Sub BtnDrawPattern_Click(sender As Object, e As EventArgs) Handles BtnDrawPattern.Click
    Dim size As Integer = Integer.Parse(txtSize.Text)
    txtPattern.Text = ""
    
    For row As Integer = 1 To size
        For col As Integer = 1 To row
            txtPattern.Text &= "* "
        Next
        txtPattern.Text &= vbCrLf
    Next
End Sub

15.3 Do Loop Structures

Do loops repeat while or until a condition is true. They offer flexibility for scenarios where the number of iterations is unknown.

15.3.1 Basic Syntax

DoLoopSyntax.vb

' Pre-test loop (condition checked before execution)
Do While condition
    ' Code to execute
Loop

Do Until condition
    ' Code to execute
Loop

' Post-test loop (condition checked after execution)
Do
    ' Code to execute
Loop While condition

Do
    ' Code to execute
Loop Until condition

15.3.2 Practical Examples

1 Input Validation

Validate user input with a Do loop:

InputValidation.vb

Private Sub BtnGetInput_Click(sender As Object, e As EventArgs) Handles BtnGetInput.Click
    Dim userInput As String
    Dim number As Integer
    Dim validInput As Boolean = False
    
    Do
        userInput = InputBox("Enter a positive number (1-100):")
        
        If Integer.TryParse(userInput, number) AndAlso number >= 1 AndAlso number <= 100 Then
            validInput = True
        Else
            MessageBox.Show("Invalid input. Please enter a number between 1 and 100.")
        End If
    Loop Until validInput
    
    MessageBox.Show($"Valid number entered: {number}")
End Sub

2 File Processing

Process lines in a file using a Do loop:

FileProcessing.vb

Private Sub BtnProcessFile_Click(sender As Object, e As EventArgs) Handles BtnProcessFile.Click
    Dim filePath As String = "C:\Data\input.txt"
    Dim line As String
    Dim lineCount As Integer = 0
    
    Using reader As New IO.StreamReader(filePath)
        Do
            line = reader.ReadLine()
            If line IsNot Nothing Then
                lineCount += 1
                ' Process the line
                lstLines.Items.Add($"Line {lineCount}: {line}")
            End If
        Loop While line IsNot Nothing
    End Using
    
    lblStatus.Text = $"Processed {lineCount} lines"
End Sub

15.4 While...End While Loop

The While loop executes as long as a condition remains true. It's a simpler alternative to Do While loops.

15.4.1 Basic Syntax

WhileSyntax.vb

While condition
    ' Code to execute
End While

15.4.2 Practical Example

Generate random numbers until a specific condition is met:

RandomNumbers.vb

Private Sub BtnGenerateRandom_Click(sender As Object, e As EventArgs) Handles BtnGenerateRandom.Click
    Dim rnd As New Random()
    Dim target As Integer = Integer.Parse(txtTarget.Text)
    Dim attempts As Integer = 0
    Dim current As Integer
    
    lstNumbers.Items.Clear()
    
    While current <> target
        current = rnd.Next(1, 101)
        attempts += 1
        lstNumbers.Items.Add($"Attempt {attempts}: {current}")
        
        ' Prevent infinite loops
        If attempts > 100 Then
            MessageBox.Show("Maximum attempts reached")
            Exit While
        End If
    End While
    
    lblResult.Text = $"Found {target} in {attempts} attempts"
End Sub

15.5 Loop Control Statements

Control loop execution with Exit and Continue statements.

1 Exit Statement

Immediately terminates loop execution:

ExitStatement.vb

For i As Integer = 1 To 100
    If i > 50 Then
        Exit For  ' Terminate loop when i exceeds 50
    End If
    ' Process value
Next

2 Continue Statement

Skips to the next iteration:

ContinueStatement.vb

For Each item In collection
    If item Is Nothing Then
        Continue For  ' Skip empty items
    End If
    ' Process item
Next

Lesson Summary

In this lesson, we've covered essential concepts about loops in VB2022:

For...Next

Ideal for fixed iterations with a counter variable

Do Loops

Flexible loops with pre-test and post-test variations

While Loops

Simple condition-first looping structure

Control Statements

Exit to terminate loops, Continue to skip iterations

Nested Loops

Loops within loops for multi-dimensional processing

These skills will help you create efficient, repetitive processes in your applications. In the next lesson, we'll explore sub procedures for organizing your code.

Exercises

Practice what you've learned with these exercises:

Exercise 1: Prime Number Finder

Create a program that:

Accepts a number from the user
Uses a loop to determine if the number is prime
Displays the result with an appropriate message

Exercise 2: Number Guessing Game

Build an application that:

Generates a random number between 1 and 100
Allows the user to guess the number
Uses a loop to continue until the correct number is guessed
Provides "too high" or "too low" feedback after each guess

Exercise 3: Fibonacci Sequence Generator

Implement a solution that:

Generates the Fibonacci sequence up to a specified number of terms
Uses a loop to calculate each term
Displays the sequence in a list box

Next Lesson

Ready to learn about organizing your code? Continue to Lesson 16: Sub Procedures in VB2022.

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