The Format Function

' All three produce the same result: "RM 1,234.57"
' 1. ToString with format specifier (most concise)
Dim price = 1234.567
lblA.Text = price.ToString("C2")                        ' "RM 1,234.57"  (culture-dependent)

' 2. String.Format -- good for building composite strings
lblB.Text = String.Format("Total: {0:C2}", price)         ' "Total: RM 1,234.57"

' 3. Interpolated string $ -- most readable, VB 2026 preferred
lblC.Text = $"Total: {price:C2}"                         ' "Total: RM 1,234.57"

' Multiple values in one interpolated string
Dim qty = 3, unitPrice = 29.99, total = qty * unitPrice
lblReceipt.Text = $"{qty} x {unitPrice:C2} = {total:C2}"   ' "3 x RM29.99 = RM89.97"

' Legacy VB6 Format() function -- still works in VB 2026
lblD.Text = Format(price, "Currency")    ' "RM 1,234.57"
lblE.Text = Format(price, "Fixed")       ' "1234.57"
lblF.Text = Format(price, "Standard")    ' "1,234.57"
lblG.Text = Format(price, "Percent")     ' "123,456.70%"

Dim n = 1234.5678

' Currency
n.ToString("C")       ' "RM 1,234.57"   (2 dp, culture symbol)
n.ToString("C0")      ' "RM 1,235"      (0 dp, rounded)
n.ToString("C4")      ' "RM 1,234.5678" (4 dp)

' Fixed-point
n.ToString("F")       ' "1234.57"
n.ToString("F0")      ' "1235"
n.ToString("F4")      ' "1234.5678"

' Number (with thousands separator)
n.ToString("N")       ' "1,234.57"
n.ToString("N0")      ' "1,235"

' Percent -- value is multiplied by 100 first
(0.1234).ToString("P")  ' "12.34%"
(0.1234).ToString("P1") ' "12.3%"
(0.1234).ToString("P0") ' "12%"

' Scientific
n.ToString("E")       ' "1.234568E+003"
n.ToString("E2")      ' "1.23E+003"
n.ToString("e4")      ' "1.2346e+003"   (lowercase e)

' General
n.ToString("G")       ' "1234.5678"  (shortest representation)
n.ToString("G4")      ' "1235"       (4 significant digits)
(0.000012345).ToString("G3")  ' "1.23E-05"  (switches to scientific)

' Integer formats
(42).ToString("D5")   ' "00042"  (zero-padded to 5 digits)
(255).ToString("X")   ' "FF"     (hexadecimal)
(255).ToString("X8")  ' "000000FF" (8-char hex, zero-padded)

Dim n = 1234.5

' 0 vs # placeholder
n.ToString("00000.00")   ' "01234.50"  -- 0 always shows digit
n.ToString("#,###.##")   ' "1,234.5"   -- # omits trailing zeros
n.ToString("#,##0.00")   ' "1,234.50"  -- standard accounting format

' Currency with RM prefix (no culture dependency)
n.ToString("'RM' #,##0.00")   ' "RM 1,234.50"

' Positive / negative / zero sections (separated by ;)
(1234.5).ToString("#,##0.00;(#,##0.00);-")    ' "1,234.50"  (positive)
(-1234.5).ToString("#,##0.00;(#,##0.00);-")   ' "(1,234.50)" (negative in parens)
(0).ToString("#,##0.00;(#,##0.00);-")         ' "-"          (zero as dash)

' Scale / k / M shorthand
(1500000).ToString("#,##0,K")    ' "1,500K"  (divide by 1,000)
(1500000).ToString("0,,M")        ' "2M"      (divide by 1,000,000)

' Phone number formatting (custom string logic)
Private Function FormatPhone(digits As String) As String
    Dim d = New String(digits.Where(Function(c) Char.IsDigit(c)).ToArray())
    If d.Length = 10 Then Return $"({d.Substring(0,3)}) {d.Substring(3,3)}-{d.Substring(6)}"
    If d.Length = 11 Then Return $"+{d(0)} ({d.Substring(1,3)}) {d.Substring(4,3)}-{d.Substring(7)}"
    Return digits     ' return as-is if unrecognised length
End Function

FormatPhone("0123456789")    ' "(012) 345-6789"
FormatPhone("60123456789")   ' "+6 (012) 345-6789"

Dim dt = New DateTime(2026, 2, 23, 15, 45, 22)   ' 23 Feb 2026 15:45:22

' Standard specifiers
dt.ToString("d")   ' "23/02/2026"          short date
dt.ToString("D")   ' "Monday, 23 February 2026"  long date
dt.ToString("t")   ' "3:45 PM"             short time
dt.ToString("T")   ' "3:45:22 PM"          long time
dt.ToString("s")   ' "2026-02-23T15:45:22" ISO 8601 (sortable)
dt.ToString("g")   ' "23/02/2026 3:45 PM"  general short

' Custom patterns -- build exactly what you need
dt.ToString("dd/MM/yyyy")           ' "23/02/2026"
dt.ToString("dd-MMM-yyyy")          ' "23-Feb-2026"
dt.ToString("dddd, d MMMM yyyy")    ' "Monday, 23 February 2026"
dt.ToString("HH:mm:ss")             ' "15:45:22"   (24-hour)
dt.ToString("hh:mm tt")             ' "03:45 PM"   (12-hour)
dt.ToString("yyyy-MM-dd HH:mm")     ' "2026-02-23 15:45"   (database-friendly)
dt.ToString("d MMM yyyy 'at' h:mmtt") ' "23 Feb 2026 at 3:45PM"

' In interpolated strings
Dim now = DateTime.Now
lblTimestamp.Text = $"Saved at {now:HH:mm:ss} on {now:dd MMM yyyy}"
lblLog.Text       = $"[{now:yyyy-MM-dd HH:mm:ss.fff}] Application started"

' DateTime components -- use properties for individual parts
lblYear.Text  = now.Year.ToString()
lblMonth.Text = now.ToString("MMMM")         ' "February"
lblDay.Text   = now.ToString("dddd")          ' "Monday"
lblWeek.Text  = now.DayOfYear.ToString()        ' day number in year

' {index,alignment:format}
' Positive alignment = right-align; Negative = left-align

' Right-align in a 10-character field
String.Format("{0,10}", "Name")     ' "      Name"  (6 spaces then "Name")
String.Format("{0,10:N2}", 1234.5)  ' "  1,234.50"  (right-aligned, 10 wide)

' Left-align
String.Format("{0,-15}", "Name")    ' "Name           " (padded right)

' Building a formatted table
Dim header = String.Format("{0,-20}{1,10}{2,10}{3,10}", "Item", "Qty", "Price", "Total")
lstReport.Items.Add(header)
lstReport.Items.Add(New String("-"c, 50))

Dim items() = {("Widget A", 5, 12.99), ("Gadget B", 2, 79.50), ("Donut C", 12, 2.50)}
For Each (name, qty, price) In items
    Dim total = qty * price
    lstReport.Items.Add(String.Format("{0,-20}{1,10}{2,10:C2}{3,10:C2}", name, qty, price, total))
Next

' Equivalent with interpolated strings ($ supports alignment too)
Dim name2 = "Widget A" : Dim qty2 = 5 : Dim price2 = 12.99
lstReport.Items.Add($"{name2,-20}{qty2,10}{price2,10:C2}{qty2*price2,10:C2}")

' PadLeft / PadRight on strings (simpler for basic padding)
"Name".PadLeft(10)          ' "      Name"
"Name".PadRight(10, "."c)   ' "Name......"
(42).ToString().PadLeft(5, "0"c)  ' "00042"

' Basic: $ prefix, {expression:format,alignment}
Dim name = "Alice" : Dim score = 92.5
$"Student: {name}, Score: {score:F1}"      ' "Student: Alice, Score: 92.5"
$"Score: {score,8:F2}"                       ' "Score:    92.50"  (right-aligned, 8 wide)

' Expressions inside braces -- any valid VB expression
Dim items = 5 : Dim unitPrice = 12.99
$"Total: {items * unitPrice:C2}"              ' "Total: RM64.95"
$"Tax (6%): {items * unitPrice * 0.06:C2}"   ' "Tax (6%): RM3.90"

' Ternary (If) inside interpolation
Dim balance = -250.0
$"Balance: {If(balance < 0, "(Overdrawn)", "")} {Math.Abs(balance):C2}"

' Calling methods inside braces
$"Hello, {name.ToUpper()}!"                  ' "Hello, ALICE!"
$"Today is {DateTime.Now:dddd, d MMMM yyyy}"  ' "Today is Monday, 23 February 2026"
$"Pi = {Math.PI:F6}"                         ' "Pi = 3.141593"

' Multi-line interpolated string (VB 2026 / C# 11 style)
Dim email = $"Dear {name},
Thank you for your order of {items} item(s).
Total charged: {items * unitPrice:C2}
Order date: {DateTime.Now:dd MMM yyyy}"

' Escape braces with {{ and }}
$"Format: {{0:C2}} produces {score:C2}"   ' "Format: {0:C2} produces RM92.50"

' Verbatim + interpolated: $@ or @$
$@"C:\Users\{name}\Documents"             ' "C:\Users\Alice\Documents" (no \\ needed)

' Invoice number: INV-2026-0042
Private Function FormatInvoiceNum(year As Integer, seq As Integer) As String
    Return $"INV-{year}-{seq:D4}"    ' D4 zero-pads to 4 digits
End Function

FormatInvoiceNum(2026, 42)    ' "INV-2026-0042"
FormatInvoiceNum(2026, 1)     ' "INV-2026-0001"

' Build complete invoice as a formatted string
Private Function BuildInvoice(customer As String, subtotal As Decimal,
                                sstRate As Double) As String
    Dim sst   = Math.Round(subtotal * CDec(sstRate), 2)
    Dim total = subtotal + sst
    Dim now   = DateTime.Now

    Return $"{'─',-44}
INVOICE  {FormatInvoiceNum(now.Year, 42),30}
{'─',-44}
Date   : {now:dd MMM yyyy}
Bill To: {customer}
{'─',-44}
Subtotal  {subtotal,26:C2}
SST {sstRate:P0,-5}   {sst,26:C2}
{'═',-44}
TOTAL     {total,26:C2}
{'─',-44}"
End Function