Creating Arrays

' Without array — tedious, error-prone, doesn't scale
Dim mark1 As Integer = 78
Dim mark2 As Integer = 92
Dim mark3 As Integer = 65
Dim mark4 As Integer = 88
Dim mark5 As Integer = 71
' Imagine 100 students — 100 Dim statements!

' With array — one name, many values, works for any size
Dim marks() As Integer = {78, 92, 65, 88, 71}

' Access by zero-based index
lblFirst.Text = marks(0).ToString()   ' 78 — index starts at 0
lblLast.Text  = marks(4).ToString()   ' 71

' Process all values with a loop — scales to any size
Dim total As Integer = 0
For i = 0 To marks.Length - 1
    total += marks(i)
Next
lblAvg.Text = $"Average: {total / marks.Length:F1}"

' ── Method 1: Declare with upper bound (5 elements: 0..4) ──
Dim scores(4)   As Integer              ' indexes 0,1,2,3,4 — all default to 0
Dim names(9)    As String               ' 10 strings, all Nothing
Dim prices(99)  As Decimal              ' 100 Decimal values

' ── Method 2: Declare and initialise with literal values ───
Dim days()  As String  = {"Mon", "Tue", "Wed", "Thu", "Fri"}
Dim primes() As Integer = {2, 3, 5, 7, 11, 13, 17}

' ── Method 3: Type inference from initialiser ─────────────
Dim colours = {"Red", "Green", "Blue"}   ' String() inferred
Dim temps   = {36.5, 37.1, 36.8}         ' Double() inferred

' Key array properties
Dim size    = scores.Length       ' 5 — total number of elements
Dim lastIdx = scores.Length - 1  ' 4 — last valid index (always Length-1)
Dim upper   = scores.GetUpperBound(0)  ' 4 — same as Length-1 for 1D

' Reading and writing elements
scores(0) = 85                    ' assign to index 0
scores(4) = 72                    ' assign to index 4 (last)
Dim first = scores(0)             ' read index 0

Dim fruits() As String = {"Apple", "Banana", "Cherry", "Durian", "Elderberry"}

' ── For loop — use when you need the index ─────────────
For i = 0 To fruits.Length - 1
    lstFruits.Items.Add($"[{i}] {fruits(i)}")
Next

' ── For Each — cleaner when you don't need the index ───
For Each fruit As String In fruits
    lstFruits.Items.Add(fruit)
Next

' ── Calculate sum and average ──────────────────────────
Dim scores() As Integer = {88, 72, 95, 61, 84}
Dim total    As Integer = 0
Dim highest  As Integer = scores(0)
Dim lowest   As Integer = scores(0)

For Each s As Integer In scores
    total  += s
    If s > highest Then highest = s
    If s < lowest  Then lowest  = s
Next

Dim average = total / scores.Length
lblStats.Text = $"Total:{total}  Avg:{average:F1}  High:{highest}  Low:{lowest}"

' ── Declare a 3×4 array (3 rows, 4 columns) ───────────────
Dim marks(2, 3) As Integer    ' rows 0..2, columns 0..3

' ── Assign values ─────────────────────────────────────────
marks(0, 0) = 85 : marks(0, 1) = 90 : marks(0, 2) = 78 : marks(0, 3) = 92
marks(1, 0) = 70 : marks(1, 1) = 65 : marks(1, 2) = 88 : marks(1, 3) = 74
marks(2, 0) = 95 : marks(2, 1) = 82 : marks(2, 2) = 76 : marks(2, 3) = 89

' ── Initialise with literal values ──────────────────────
Dim grid(,) As Integer = {{85,90,78,92},
                          {70,65,88,74},
                          {95,82,76,89}}

' ── Nested loops to process all cells ───────────────────
Dim rows    = grid.GetLength(0)   ' 3 rows
Dim cols    = grid.GetLength(1)   ' 4 columns

For r = 0 To rows - 1
    Dim rowTotal As Integer = 0
    For c = 0 To cols - 1
        rowTotal += grid(r, c)
    Next
    Dim avg = rowTotal / cols
    lstResults.Items.Add($"Student {r + 1}: Total={rowTotal}  Avg={avg:F1}")
Next

Dim nums() As Integer = {42, 7, 98, 15, 63, 28}

' ── Sort ascending ──────────────────────────────────────
Array.Sort(nums)
' nums is now: {7, 15, 28, 42, 63, 98}

' ── Reverse (descending after sort) ─────────────────────
Array.Reverse(nums)
' nums is now: {98, 63, 42, 28, 15, 7}

' ── Linear search ───────────────────────────────────────
Dim idx = Array.IndexOf(nums, 42)   ' returns 2 (position of 42)
If idx >= 0 Then
    lblFind.Text = $"Found 42 at index {idx}"
Else
    lblFind.Text = "Not found"
End If

' ── Binary search (array must be sorted first) ──────────
Array.Sort(nums)
Dim pos = Array.BinarySearch(nums, 42)   ' much faster for large arrays

' ── Resize — change number of elements ──────────────────
Array.Resize(nums, 10)         ' grows to 10; new elements = 0
Array.Resize(nums, 3)          ' shrinks to 3; excess discarded

' ── Copy ────────────────────────────────────────────────
Dim backup(5) As Integer
Array.Copy(nums, backup, nums.Length)    ' full copy

' ── Fill (new in .NET 10) ───────────────────────────────
Dim zeros(9) As Integer
Array.Fill(zeros, -1)          ' fill all 10 elements with -1

' Declare without size — no elements yet
Dim names() As String

' ── ReDim — set or change size (discards existing data) ─
ReDim names(4)           ' now has 5 elements (0..4)
names(0) = "Alice"
names(1) = "Bob"
names(2) = "Charlie"

' ── ReDim Preserve — resize AND keep existing values ────
ReDim Preserve names(6)   ' grows to 7; Alice/Bob/Charlie preserved
names(3) = "Diana"
names(4) = "Eve"

' ── Common pattern: grow array by 1 when user adds item ─
Private _items() As String
Private _count   As Integer = 0

Private Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
    ReDim Preserve _items(_count)          ' grow by one slot
    _items(_count) = txtItem.Text.Trim()   ' store in new slot
    _count += 1
    lstItems.Items.Add(_items(_count - 1))
    txtItem.Clear()
End Sub

' ── Create a List(Of T) ─────────────────────────────────
Dim students As New List(Of String)()
Dim scores   As New List(Of Integer)()

' ── Add items ───────────────────────────────────────────
students.Add("Alice")
students.Add("Bob")
students.Add("Charlie")
students.AddRange({"Diana", "Eve"})

' ── Access by index (same as arrays) ───────────────────
Dim first = students(0)     ' "Alice"
Dim count = students.Count  ' 5

' ── Remove items ────────────────────────────────────────
students.Remove("Bob")         ' remove by value
students.RemoveAt(0)           ' remove by index

' ── Search ──────────────────────────────────────────────
Dim exists = students.Contains("Charlie")          ' True
Dim idx    = students.IndexOf("Diana")             ' returns index

' ── Sort and iterate ────────────────────────────────────
students.Sort()
For Each name As String In students
    lstNames.Items.Add(name)
Next

' ── Convert between array and List ─────────────────────
Dim arr()     = students.ToArray()           ' List → array
Dim backToList = New List(Of String)(arr)   ' array → List

Imports System.Linq

Dim scores() As Integer = {88, 72, 95, 61, 84, 55, 91, 67}

' ── Aggregate queries ───────────────────────────────────
Dim highest  = scores.Max()             ' 95
Dim lowest   = scores.Min()             ' 55
Dim average  = scores.Average()         ' 76.625
Dim total    = scores.Sum()             ' 613

' ── Filter with Where ───────────────────────────────────
Dim passed  = scores.Where(Function(s) s >= 50).ToArray()
' {88, 72, 95, 61, 84, 55, 91, 67}

Dim honours = scores.Where(Function(s) s >= 75).ToArray()
' {88, 95, 84, 91}

' ── Sort with OrderBy / OrderByDescending ───────────────
Dim ascending  = scores.OrderBy(Function(s) s).ToArray()
Dim descending = scores.OrderByDescending(Function(s) s).ToArray()

' ── Transform with Select ───────────────────────────────
Dim doubled    = scores.Select(Function(s) s * 2).ToArray()
Dim grades     = scores.Select(Function(s) If(s >= 75, "Pass", "Fail")).ToArray()

' ── Count with condition ────────────────────────────────
Dim passCount  = scores.Count(Function(s) s >= 50)    ' 8
Dim failCount  = scores.Count(Function(s) s < 50)     ' 0

' ── Display results ─────────────────────────────────────
lblStats.Text = $"Max:{highest}  Min:{lowest}  Avg:{average:F1}  Passed:{passCount}"
lstHonours.DataSource = honours