String Manipulation

' ── & operator — safe, always concatenates ─────────────
Dim firstName As String = "Alice"
Dim lastName  As String = "Wong"
Dim fullName  = firstName & " " & lastName   ' "Alice Wong"

' ── + operator — risky with mixed types ────────────────
Dim result1 = "Score: " + 95.ToString()     ' ✔ OK — explicit ToString()
Dim result2 = "Value: " & 42               ' ✔ & converts 42 to "42" automatically

' ── String interpolation — the modern VB 2026 way ──────
Dim age   = 25
Dim score = 95
Dim gpa   = 3.85

lblInfo.Text = $"{firstName} {lastName} — Age: {age}, Score: {score}, GPA: {gpa:F2}"
' → "Alice Wong — Age: 25, Score: 95, GPA: 3.85"

' Interpolation with expressions and format specs
Dim price = 29.9D
lblPrice.Text = $"Total: {price * 1.06:C}"     ' currency format → "Total: RM31.65"
lblDate.Text  = $"Today: {DateTime.Today:dd/MM/yyyy}"

' ── += to append to existing string ────────────────────
Dim report As String = ""
report &= "Name: Alice" & vbCrLf
report &= "Score: 95"  & vbCrLf
txtReport.Text = report

Dim s = "Visual Basic 2026"

' ── VB functions — 1-based ─────────────────────────────
Dim vbLen   = Len(s)                  ' 17
Dim vbLeft  = Left(s, 6)             ' "Visual" (first 6 chars)
Dim vbRight = Right(s, 4)            ' "2026" (last 4 chars)
Dim vbMid   = Mid(s, 8, 5)           ' "Basic" (start at pos 8, take 5)
Dim vbFind  = InStr(s, "Basic")       ' 8 (1-based position)

' ── .NET String methods — 0-based ─────────────────────
Dim netLen    = s.Length              ' 17
Dim netLeft   = s.Substring(0, 6)    ' "Visual" (start 0, length 6)
Dim netRight  = s.Substring(s.Length - 4)   ' "2026"
Dim netMid    = s.Substring(7, 5)    ' "Basic" (0-based start = 7)
Dim netFind   = s.IndexOf("Basic")   ' 7 (0-based index)

' ── Consistency tip: pick one style and stick to it ────
' .NET methods work everywhere; VB functions need Imports Microsoft.VisualBasic

Dim email = "[email protected]"

' ── Contains / StartsWith / EndsWith ──────────────────
If email.Contains("@") Then
    lblResult.Text = "Valid email format"
End If

If email.EndsWith(".com") Then
    lblDomain.Text = "Commercial domain"
End If

' ── IndexOf — find position (0-based), -1 if not found ─
Dim atPos  = email.IndexOf("@")           ' 10
Dim dotPos = email.LastIndexOf(".")         ' 18 (last dot)

' Extract username and domain using IndexOf
If atPos > 0 Then
    Dim username = email.Substring(0, atPos)           ' "alice.wong"
    Dim domain   = email.Substring(atPos + 1)           ' "example.com"
    lblUser.Text   = $"User: {username}"
    lblDomain.Text = $"Domain: {domain}"
End If

' ── InStr — VB-style search (1-based, 0 if not found) ─
Dim pos = InStr(email, "@")              ' 11 (1-based)
If pos > 0 Then
    Dim user = Left(email, pos - 1)        ' "alice.wong"
End If

' ── Case-insensitive comparison ────────────────────────
If String.Compare(email, "[email protected]", True) = 0 Then
    ' Third arg True = ignore case
End If

' ── OrdinalIgnoreCase (most reliable for comparisons) ──
If email.Equals("[email protected]", StringComparison.OrdinalIgnoreCase) Then
    lblResult.Text = "Emails match (case-insensitive)"
End If

Dim input = "  Hello, Visual Basic 2026!  "

' ── Case conversion ────────────────────────────────────
Dim upper  = input.ToUpper()           ' "  HELLO, VISUAL BASIC 2026!  "
Dim lower  = input.ToLower()           ' "  hello, visual basic 2026!  "
Dim proper = StrConv(input, VbStrConv.ProperCase)   ' "  Hello, Visual Basic 2026!  "

' ── Trim whitespace ────────────────────────────────────
Dim trimmed  = input.Trim()            ' "Hello, Visual Basic 2026!" (both ends)
Dim trimLeft = input.TrimStart()       ' removes leading spaces only
Dim trimEnd  = input.TrimEnd()         ' removes trailing spaces only
' Good practice: always Trim() user input from TextBoxes
Dim name = txtName.Text.Trim()

' ── Replace ────────────────────────────────────────────
Dim phone   = "012-345-6789"
Dim noHyphen = phone.Replace("-", "")   ' "0123456789" — remove all hyphens
Dim masked   = phone.Replace(phone.Substring(3, 3), "***")  ' mask middle digits

' ── PadLeft / PadRight ─────────────────────────────────
Dim id      = "42"
Dim padded  = id.PadLeft(6, "0"c)        ' "000042" — zero-pad to 6 digits
Dim padR    = "Alice".PadRight(12, "."c)  ' "Alice......." — table alignment

' ── Reverse a string (no built-in, use LINQ) ───────────
Dim rev = New String(input.Trim().Reverse().ToArray())
' → "!6202 cisaB lausiV ,olleH"

' ── Split by single delimiter ──────────────────────────
Dim csv     = "Alice,Bob,Charlie,Diana,Eve"
Dim names() = csv.Split(","c)               ' {"Alice","Bob","Charlie","Diana","Eve"}

For Each name As String In names
    lstNames.Items.Add(name)
Next

' ── Split with multiple delimiters ────────────────────
Dim data    = "Name:Alice;Age:25;City:KL"
Dim pairs() = data.Split({";"c, ":"c})       ' {"Name","Alice","Age","25","City","KL"}

' ── Split with options — remove empty entries ──────────
Dim messy   = "one,,two,,,three"
Dim clean() = messy.Split({","c}, StringSplitOptions.RemoveEmptyEntries)
' {"one","two","three"} — empty parts removed

' ── Parse CSV line into structured data ────────────────
Dim record  = "STU001,Alice Wong,85,92,78"
Dim fields  = record.Split(","c)
Dim id      = fields(0)              ' "STU001"
Dim student = fields(1)             ' "Alice Wong"
Dim mark1   = CInt(fields(2))        ' 85

' ── Join — reverse of split ────────────────────────────
Dim parts() = {"Visual", "Basic", "2026"}
Dim joined  = String.Join(" ", parts)    ' "Visual Basic 2026"
Dim path    = String.Join("/", {"C:", "Users", "Alice", "Documents"})
' "C:/Users/Alice/Documents"

' ── Split path components ──────────────────────────────
Dim filePath  = "C:\Users\Alice\report.docx"
Dim pathParts = filePath.Split("\"c)
Dim fileName  = pathParts(pathParts.Length - 1)   ' "report.docx"

Imports System.Text

' ── The SLOW way — creates thousands of string objects ─
Dim report As String = ""
For i = 1 To 1000
    report &= $"Line {i}: data{vbCrLf}"    ' ✘ slow — 1000 new string objects
Next

' ── The FAST way — StringBuilder with mutable buffer ───
Dim sb As New StringBuilder()
For i = 1 To 1000
    sb.AppendLine($"Line {i}: data")        ' ✔ fast — appends to internal buffer
Next
Dim result = sb.ToString()                  ' one string at the end

' ── StringBuilder methods ──────────────────────────────
Dim sb2 As New StringBuilder("Hello")
sb2.Append(", World")                       ' "Hello, World"
sb2.AppendLine("!")                          ' appends + newline
sb2.Insert(5, " Beautiful")                ' "Hello Beautiful, World\n!"
sb2.Replace("World", "VB 2026")            ' find/replace in buffer
sb2.Remove(0, 6)                            ' remove 6 chars from pos 0
Dim len = sb2.Length                          ' current length
sb2.Clear()                                   ' reset to empty

' ── Practical: generate HTML table ────────────────────
Dim html As New StringBuilder()
html.AppendLine("<table>")
For Each row As String In dataRows
    html.AppendLine($"  <tr><td>{row}</td></tr>")
Next
html.AppendLine("</table>")
txtOutput.Text = html.ToString()

' ── Raw string literals (multi-line, no escape needed) ─
Dim json = """
{
    "name": "Alice",
    "age": 25,
    "city": "Kuala Lumpur"
}
"""
' Triple quotes — no need to escape internal quotes

' ── String.Equals with OrdinalIgnoreCase ───────────────
Dim isMatch = "Hello".Equals("hello", StringComparison.OrdinalIgnoreCase)   ' True

' ── Span-based methods — zero-allocation parsing ───────
Dim line   = "Alice,25,KL".AsSpan()
Dim comma1 = line.IndexOf(","c)
Dim name   = line.Slice(0, comma1).ToString()   ' "Alice" — no string allocation

' ── String.Create — efficient string construction ──────
Dim id = String.Create(8, "user", Sub(span, prefix)
    prefix.CopyTo(span)
    "0001".CopyTo(span.Slice(prefix.Length))
End Sub)
' id = "user0001" — no intermediate strings

' ── SearchValues — fast multi-char scanning (.NET 10) ──
Dim digits   = System.Buffers.SearchValues.Create("0123456789")
Dim phone    = "Call 012-345-6789 now"
Dim firstNum = phone.AsSpan().IndexOfAny(digits)    ' 5 — first digit position

' ── String.IsNullOrWhiteSpace — essential input guard ──
If String.IsNullOrWhiteSpace(txtName.Text) Then
    lblError.Text = "Name is required"
    Return
End If