Lesson 8: Mastering Select Case Statements

Learn how to simplify decision-making in VB6 with clean, efficient case structures

Key Takeaway

Select Case statements provide a cleaner, more efficient way to handle multiple conditions compared to nested If...Then...ElseIf statements. Master this structure to create more readable and maintainable VB6 applications.

Welcome to Lesson 8 of our Visual Basic 6 Tutorial! In this lesson, you'll master VB6's powerful Select Case structure that provides a cleaner alternative to complex If...Then...ElseIf statements when evaluating a single expression against multiple possible values.

8.1 Introduction to Select Case

The Select Case control structure is designed to simplify decision-making when you need to compare a single expression against multiple possible values. It's particularly useful for:

Evaluating a variable against multiple constant values
Replacing complex If-ElseIf chains
Handling menu selections or command options
Processing categorized data (grades, statuses, etc.)

Figure 8.1: Select Case Flow Chart

Start

Begin Select Case execution

Evaluate Expression

Calculate the value to compare

Compare to Case Values

Check against each Case condition in order
Case Value1, Case Value2, ... Case ValueN

Execute Matching Block

Run the code for the first matching Case
If no match found, execute Case Else block

End Select

Continue with program execution

How Select Case Works

The Select Case statement evaluates an expression once and then compares it against multiple Case conditions. When it finds a matching Case, it executes the associated code block and then exits the Select Case structure. If no match is found, the Case Else block (if present) is executed. This structure is more efficient than multiple If...ElseIf statements when testing the same expression against multiple values.

Expression Evaluation

The expression is evaluated only once at the beginning of the Select Case statement.

Sequential Checking

Case conditions are checked in the order they appear in the code.

Single Execution

Only the first matching Case block is executed, even if multiple Cases match.

8.2 Select Case Syntax

The basic structure of the Select Case statement:

SelectCaseSyntax.vb

Select Case expression
    Case value1
        ' Code to execute if expression = value1
    Case value2
        ' Code to execute if expression = value2
    Case value3
        ' Code to execute if expression = value3
    Case Else
        ' Code to execute if no match is found
End Select

Important Note

Always include a Case Else block to handle unexpected values. This makes your code more robust and prevents unexpected behavior.

Example 1: Grade Evaluation

GradeEvaluator.vb

Private Sub Compute_Click()
    Dim grade As String
    grade = txtGrade.Text

    Select Case grade
        Case "A"
            result.Caption = "High Distinction"
        Case "A-"
            result.Caption = "Distinction"
        Case "B"
            result.Caption = "Credit"
        Case "C"
            result.Caption = "Pass"
        Case Else
            result.Caption = "Fail"
    End Select
End Sub

Grade Evaluator:

Enter Grade (A, A-, B, C):

Result: Credit

8.3 Advanced Case Expressions

Select Case supports more complex expressions including ranges, multiple values, and comparisons:

Expression Type	Syntax	Example
Single Value	`Case value`	`Case "A"`
Multiple Values	`Case value1, value2`	`Case "Mon", "Tue"`
Range	`Case start To end`	`Case 1 To 10`
Comparison	`Case Is operator value`	`Case Is >= 50`
Combination	`Case value1, value2 To value3, Is operator value`	`Case 1, 3 To 7, Is > 10`

Example 2: Mark Evaluation with Ranges

MarkEvaluator.vb

Private Sub Compute_Click()
    Dim mark As Single
    mark = Val(txtMark.Text)

    Select Case mark
        Case Is >= 85
            comment.Caption = "Excellence"
        Case 70 To 84
            comment.Caption = "Good"
        Case 60 To 69
            comment.Caption = "Above Average"
        Case 50 To 59
            comment.Caption = "Average"
        Case Else
            comment.Caption = "Need to work harder"
    End Select
End Sub

Figure 8.2: Mark Evaluation Form

Mark Evaluator

Enter Student Mark:

Result:

Figure 8.3: Evaluation Result

📊

Student Performance

Excellence

Example 3: Number Guessing Game

NumberGame.vb

Dim Secret_Number As Integer

Private Sub Guess_Click()
    Dim Your_Number As Integer
    Your_Number = Val(InputBox("Enter a number between 1 and 6 inclusive"))

    Select Case Your_Number
        Case Is < Secret_Number
            MsgBox "Your number is smaller than the secret number, try again!"
        Case Is > Secret_Number
            MsgBox "Your number is greater than the secret number, try again!"
        Case Else
            Beep
            MsgBox "Your number is correct, congratulations!"
    End Select
End Sub

Private Sub Form_Load()
    Randomize
    Secret_Number = 1 + Int(6 * Rnd)
End Sub

Example 4: Day Classifier NEW

DayClassifier.vb

Private Sub CheckDay_Click()
    Dim day As String
    day = txtDay.Text

    Select Case day
        Case "Monday", "Tuesday", "Wednesday", "Thursday", "Friday"
            result.Caption = "Weekday"
        Case "Saturday", "Sunday"
            result.Caption = "Weekend"
        Case Else
            result.Caption = "Invalid day"
    End Select
End Sub

Example 5: Discount Calculator NEW

DiscountCalculator.vb

Private Sub Calculate_Click()
    Dim age As Integer
    Dim membership As String
    
    age = Val(txtAge.Text)
    membership = txtMembership.Text
    
    ' Using Select Case True for complex conditions
    Select Case True
        Case age < 18
            discount.Caption = "0% (Under 18)"
        Case age >= 65 And membership = "Gold"
            discount.Caption = "25% (Senior Gold Member)"
        Case age >= 65
            discount.Caption = "15% (Senior)"
        Case membership = "Gold"
            discount.Caption = "20% (Gold Member)"
        Case membership = "Silver"
            discount.Caption = "10% (Silver Member)"
        Case Else
            discount.Caption = "5% (Standard)"
    End Select
End Sub

Advanced Technique

Using Select Case True allows evaluating multiple Boolean expressions, providing great flexibility for complex conditional logic.

Lesson Summary

In this lesson, you've mastered the Select Case structure in VB6:

Cleaner Decision-Making

Select Case provides a more readable alternative to complex If-ElseIf chains.

Multiple Value Handling

Use commas to test multiple values in a single Case statement.

Range Evaluation

Use the To keyword to test value ranges.

Comparison Operators

Use Is with operators like >=, <, etc. for comparisons.

Case Else

Always include to handle unexpected values and make your code robust.

Best Practice

Use Select Case when evaluating a single expression against multiple values. For complex conditions with multiple variables, If statements might be more appropriate.

Practice Exercises

Test your understanding of Select Case with these exercises:

Exercise 1: Season Classifier

Create a program that takes a month number (1-12) and uses Select Case to display the corresponding season:

December, January, February: Winter
March, April, May: Spring
June, July, August: Summer
September, October, November: Fall

Exercise 2: Shipping Calculator

Create a shipping cost calculator based on package weight:

0-1 kg: $5.00
1.1-5 kg: $10.00
5.1-10 kg: $15.00
Over 10 kg: $15 + $1.50 per additional kg

Use Select Case for the base rates and handle the over 10kg case separately.

Exercise 3: User Role Permissions

Implement a system that displays permissions based on user role codes:

A: Full Administrative Access
M: Manager Access (Create, Edit, Delete)
E: Editor Access (Create, Edit)
V: Viewer Access (Read Only)
Default: No Access

Use a Select Case statement to evaluate the role code.

Next Lesson

Continue your VB6 journey with Lesson 9: Looping Structures.

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