Quiz 4 Study Guide — Making Decisions

Chapter 4: Making Decisions

4.1 Decision Structures

Decision structures (selection structures) let code choose between alternative actions
If...Then is the simplest: If condition Then action
Conditions use relational operators: =, <>, <, >, <=, >=
Conditions evaluate to True or False — Boolean expressions
Decisions control program flow at runtime

4.2 If...Then Statements

Syntax: If condition Then statement
Single-line: If intTemperature > 40 Then lblMessage.Text = "Warm day"
Multi-line: If condition Then ... End If
Use comparison on controls: txtInput.Text, numeric values
Val() function converts string to number: Val(txtAge.Text)

4.3 If...Then...Else

Syntax: If condition Then ... Else ... End If
Handles both true and false branches
If intScore >= 70 Then lblGrade.Text = "Pass" Else lblGrade.Text = "Fail" End If
Can contain multiple statements in each block
Only ONE branch executes — never both

4.4 Nested If Statements

An If block inside another If block (or Else block)
Used for multi-level decisions: A → B → C
If condition1 Then ... If condition2 Then ... End If ... End If
Be careful with matching End If for each level
Indentation is critical for readability

4.5 Logical Operators

And: both conditions must be True
Or: at least one condition must be True
Not: reverses True↔False (Not condition)
Xor: exactly one must be True (rarely used)
AndAlso / OrElse — short-circuit evaluation (VB.NET, not classic VB)

4.6 Comparing Strings

Strings compared alphabetically (lexicographically)
Case-sensitive by default: "Hello" <> "hello"
Use UCase() or LCase() to normalize: UCase(strA) = UCase(strB)
String.Compare(strA, strB, True) — True = ignore case
Option Compare Text changes default to case-insensitive

4.7 Select Case

Alternative to nested If for multiple distinct values
Syntax: Select Case expression ... Case value ... Case Else ... End Select
Case 1 To 5 — range
Case Is >= 90 — comparison with Is keyword
Case "A", "B" — multiple values (comma-separated)
Case Else — optional catch-all (like default)

4.8 Input Validation

Validate user input before processing
Check for empty text: txtInput.Text = "" or txtInput.Text.Length = 0
Check numeric input: IsNumeric(txtInput.Text)
Use TryParse for type-safe checking: Integer.TryParse(txtInput.Text, num)
Provide feedback (MessageBox) for invalid input
Prevent crashes from bad data at runtime

💡 Key Tip: Practice tracing through If/Then/Else and Select Case blocks by hand. Write down what each line does before running. This is the #1 way to prepare for decision-structure questions.

📝 Practice Quiz — Chapter 4

10 questions. Select your answer, then check the result. All key concepts from Chapter 4.

🃏 Flashcards — Chapter 4

20 cards. Click the card to flip. Use buttons to navigate.

Press a button to start

Card 1 of 20

📋 Cheat Sheet — Chapter 4

🔑 Decision Structure Syntax

If condition Then
    statements
End If

If condition Then
    statements
Else
    statements
End If

If condition1 Then
    If condition2 Then
        statements
    End If
End If

🔑 Logical Operators

A And B     → True only if BOTH are True
A Or B      → True if EITHER is True
Not A       → Flips True↔False
A Xor B     → True if EXACTLY ONE is True

🔑 Select Case

Select Case expression
    Case value1
        ' code
    Case 1 To 5       ' range
    Case Is >= 90     ' comparison
    Case "A", "B"    ' multiple values
    Case Else         ' catch-all
End Select

🔑 Input Validation

' Check for empty
If txtInput.Text = "" Then
    MessageBox.Show("Enter a value")
End If

' Check if numeric
If IsNumeric(txtInput.Text) Then
    ' safe to use Val()
End If

' Best: TryParse
Dim num As Integer
If Integer.TryParse(txtInput.Text, num) Then
    ' num has the value
Else
    MessageBox.Show("Invalid number")
End If

🔑 String Comparison

Case-sensitive: "Hello" = "HELLO" → False
Ignore case: UCase("Hello") = UCase("HELLO") → True
Option Compare Text → makes all comparisons case-insensitive

Tip: If the quiz has code traces, write the variable values on scratch paper as you step through each line.