📚 Exam 1 Study Guide

1.1 Computer Systems

Hardware (CPU, memory, storage, I/O) + Software (OS, applications). Programs are sets of instructions that tell the computer what to do.

• CPU — Central Processing Unit, the "brain"
• RAM — volatile memory, lost on shutdown
• Hard drive/SSD — persistent storage

1.2 Programs & Programming Languages

Low-level (machine language, assembly) → High-level (VB, Python, Java). Source code → Compiler/Interpreter → Machine code.

• Syntax: rules of the language
• Compiler: translates all at once
• Interpreter: translates line by line

1.3 More About Controls

Form design in Visual Studio IDE. Common controls: Button, Label, TextBox, PictureBox.

• Properties: Text, Name, Size, Location, BackColor, ForeColor, Font
• Events: Click, Load, TextChanged, MouseEnter/MouseLeave

1.4 The Programming Process

1. Analyze requirements → 2. Design UI → 3. Write code → 4. Test → 5. Debug → 6. Deploy

1.5 Visual Studio

IDE features: Solution Explorer, Properties window, Toolbox, Code Editor, Error List, Debugger.

2.1 Problem Solving

Steps: Understand → Plan → Design UI → Code → Test

2.2 Building the Directions App

Create form, add controls, set properties, write event handlers.

2.3 Responding to Events

Event-driven programming. Private Sub btnName_Click(sender, e) Handles btnName.Click

• Event handler = method that runs when an event occurs
• The Handles keyword connects the handler to the control/event

2.4-2.5 Modifying Properties in Code

controlName.PropertyName = value — e.g. lblOutput.Text = "Hello"

• AutoSize: control shrinks/grows to fit content
• BorderStyle: None, FixedSingle, Fixed3D
• TextAlign: TopLeft, TopCenter, TopRight, MiddleLeft, etc.

3.1 TextBox Input

txtInput.Text returns a string. Must convert for math: CDec(txtInput.Text) or Decimal.Parse(txtInput.Text).

3.2 Variables & Data Types

Dim name As String
Dim age As Integer = 25
Dim price As Decimal = 19.99D
Dim flag As Boolean = True

3.3 Arithmetic & Precedence

PEMDAS: Parentheses → Exponents → Multiplication/Division → Addition/Subtraction

^   Exponentiation
*   Multiplication
/   Division (returns Double)
\   Integer Division
Mod Modulus (remainder)
+   Addition
-   Subtraction

3.4 Type Conversion & Option Strict

Option Strict On (recommended) — forces explicit conversions. Use conversion functions: CInt(), CDec(), CDbl(), CStr(), CBool(), Val() (returns Double from string).

Implicit conversion = narrowing (data loss possible). Explicit conversion = using conversion functions.

3.5 Formatting (ToString)

price.ToString("C")   → $19.99 (currency)
num.ToString("N")    → 1,234.57 (number)
num.ToString("P")    → 12.34% (percent)
num.ToString("F2")   → 123.46 (fixed, 2 decimals)

3.6 Class-Level Variables

Declared at the form level (before any Sub or Function), accessible from all procedures in the class. Use Private or Dim in the declarations section.

3.7 Exception Handling

Try
    ' Code that might cause an error
    result = CDec(txtInput.Text)
Catch ex As Exception
    MessageBox.Show("Invalid input: " & ex.Message)
Finally
    ' Runs whether error or not
End Try

4.1-4.2 If...Then Statements

If condition Then
    ' Code runs if True
End If

Relational operators: = <> < > <= >=

4.3 If...Then...Else

If score >= 70 Then
    lblResult.Text = "Pass"
Else
    lblResult.Text = "Fail"
End If

ElseIf for multiple conditions:

If grade >= 90 Then
    letter = "A"
ElseIf grade >= 80 Then
    letter = "B"
ElseIf grade >= 70 Then
    letter = "C"
Else
    letter = "F"
End If

4.4 Nested If

If statements inside other If statements:

If loggedIn Then
    If isAdmin Then
        lblMsg.Text = "Admin panel"
    Else
        lblMsg.Text = "User panel"
    End If
End If

4.5 Logical Operators

And     Both True
Or      Either True
Not     Reverses True/False
Xor     Exactly one True
AndAlso Short-circuit AND (stops evaluating if first is False)
OrElse  Short-circuit OR (stops evaluating if first is True)

4.6 Comparing Strings

Option Compare Text — case-insensitive
Option Compare Binary — case-sensitive (default)

If name.ToUpper() = "JOHN" Then
    ' Case-insensitive comparison

If String.Compare(str1, str2, ignoreCase:=True) = 0 Then
    ' Another way

4.7 Select Case

Select Case grade
    Case 90 To 100
        letter = "A"
    Case 80 To 89
        letter = "B"
    Case 70 To 79
        letter = "C"
    Case "F", "D"
        letter = Nothing
    Case Else
        letter = "Invalid"
End Select

4.8 Input Validation

• TryParse: Decimal.TryParse(txtInput.Text, result) — returns True/False
• Try/Catch: handle conversion errors
• IsNumeric: If IsNumeric(txtInput.Text) Then (older approach)
• Check for empty: If txtInput.Text = "" Then or If String.IsNullOrEmpty(txtInput.Text) Then