Understanding Data Types

' Integer — whole numbers, most common choice
Dim age       As Integer = 25
Dim score     As Integer = -150
Dim maxItems  As Integer = 2_147_483_647   ' digit separator for readability (.NET 10)

' Long — when Integer isn't big enough
Dim population As Long = 7_900_000_000L  ' world population — exceeds Integer limit
Dim fileBytes  As Long = 1_073_741_824L  ' 1 GB in bytes

' Double — decimal numbers, ~15 significant digits
Dim height     As Double = 1.75
Dim pi         As Double = 3.14159265358979
Dim gravity    As Double = 9.80665

' Decimal — EXACT precision for money calculations
Dim price      As Decimal = 19.99D          ' D suffix = Decimal literal
Dim taxRate    As Decimal = 0.06D
Dim total      As Decimal = price * (1D + taxRate)

' Type inference — compiler deduces type from value (.NET 10)
Dim quantity  = 42           ' inferred as Integer
Dim rate      = 3.14         ' inferred as Double
Dim name      = "Alice"      ' inferred as String

' String declaration
Dim firstName  As String = "Alice"
Dim lastName   As String = "Wong"
Dim empty      As String = ""               ' empty string
Dim nothing    As String = Nothing          ' null reference

' String interpolation (preferred in VB 2026)
Dim greeting  As String = $"Hello, {firstName} {lastName}!"

' String functions
Dim upper     = firstName.ToUpper()           ' "ALICE"
Dim length    = firstName.Length               ' 5
Dim trimmed   = "  hello  ".Trim()           ' "hello"
Dim contains  = firstName.Contains("lic")    ' True

' Char — single character
Dim initial  As Char = "A"c                 ' c suffix = Char literal
Dim firstChar = firstName(0)                  ' "A" — index access

' Test for empty/null safely
If String.IsNullOrWhiteSpace(firstName) Then
    lblStatus.Text = "Name is required."
End If

Dim isLoggedIn   As Boolean = False
Dim hasPermission As Boolean = True
Dim isAdult       As Boolean = (age >= 18)    ' result of comparison

' Logical operators
Dim canAccess = isLoggedIn AndAlso hasPermission  ' short-circuit And
Dim needsHelp = Not isLoggedIn OrElse Not hasPermission

' Toggle a flag
isLoggedIn = Not isLoggedIn

' Use in If statement
If canAccess Then
    lblWelcome.Text = "Welcome!"
Else
    lblWelcome.Text = "Access denied."
End If

' Date literals — use # delimiters
Dim independence As Date = #8/31/1957#         ' Malaysia Independence Day
Dim newYear      As Date = #1/1/2026 12:00:00 AM#

' Current date/time
Dim now     As Date = DateTime.Now             ' local date + time
Dim today   As Date = DateTime.Today           ' date only, time = 00:00

' Accessing parts
Dim yr   = now.Year       ' e.g. 2026
Dim mo   = now.Month      ' 1–12
Dim dy   = now.Day        ' 1–31
Dim hr   = now.Hour       ' 0–23

' Date arithmetic
Dim deadline     = today.AddDays(30)           ' 30 days from now
Dim nextMonth    = today.AddMonths(1)
Dim daysSince    = (today - independence).TotalDays

' Formatting
Dim formatted    = now.ToString("dd/MM/yyyy")  ' "22/02/2026"
Dim withTime     = now.ToString("dd MMM yyyy hh:mm tt")
lblDate.Text     = $"Today is: {formatted}"

' Parsing a date from a string
Dim parsed As Date
If Date.TryParse(txtDate.Text, parsed) Then
    lblResult.Text = $"Valid date: {parsed:dd/MM/yyyy}"
Else
    lblResult.Text = "Invalid date entered."
End If

' Unsafe — throws FormatException if user types "abc"
Dim bad = CInt(txtInput.Text)   ' ❌ avoid for user input

' Safe — TryParse returns True/False, never throws
Dim value As Integer
If Integer.TryParse(txtInput.Text, value) Then
    lblResult.Text = $"Valid integer: {value}"
Else
    lblResult.Text = "⚠ Please enter a whole number."
    lblResult.ForeColor = Color.Red
End If

' Double.TryParse — for decimal input
Dim amount As Double
If Double.TryParse(txtPrice.Text, amount) Then
    lblTotal.Text = $"Total: {amount * 1.06:F2}"
End If

' Converting number to string for display
Dim count  As Integer = 5
Dim msg    = $"You have {count} messages."   ' implicit String conversion in interpolation
Dim text   = count.ToString()                  ' explicit
Dim formatted = count.ToString("N0")          ' "5" with thousands separator

' Byte max is 255 — going over causes OverflowException
Dim b As Byte = 255
b += 1  ' ❌ OverflowException at runtime!

' Integer max is 2,147,483,647
Dim n As Integer = Integer.MaxValue   ' 2,147,483,647
n += 1  ' ❌ OverflowException

' Solution 1 — use a bigger type (Long)
Dim safe As Long = Integer.MaxValue
safe += 1   ' ✅ 2,147,483,648 — no overflow

' Solution 2 — check before computing
If n < Integer.MaxValue Then
    n += 1
Else
    MsgBox("Value would overflow!")
End If

' Useful constants provided by .NET
Dim intMin = Integer.MinValue    ' -2,147,483,648
Dim intMax = Integer.MaxValue    '  2,147,483,647
Dim dblMax = Double.MaxValue     '  1.7976... × 10³⁰⁸

' Type inferred from literal value
Dim count    = 10          ' Integer
Dim price    = 9.99        ' Double
Dim name     = "Alice"     ' String
Dim flag     = True        ' Boolean

' Type inferred from method return value
Dim today    = DateTime.Today          ' Date
Dim items    = New List(Of String)()  ' List(Of String)

' Digit separators for readability (new in .NET 10)
Dim million  = 1_000_000
Dim pi       = 3.141_592_653_589_793
Dim binary   = &B1111_0000    ' binary literal = 240
Dim hex      = &HFF_FF        ' hex literal = 65535

' Nullable types — value OR Nothing
Dim maybeAge  As Integer? = Nothing   ' ? means nullable
If maybeAge.HasValue Then
    lblAge.Text = maybeAge.Value.ToString()
Else
    lblAge.Text = "Age not provided"
End If

' Null-coalescing — default if Nothing
Dim displayAge = maybeAge ?? 0      ' returns 0 if maybeAge is Nothing