Math Operations

Dim x As Integer = 10

x += 5   ' same as: x = x + 5   → x = 15
x -= 3   ' same as: x = x - 3   → x = 12
x *= 2   ' same as: x = x * 2   → x = 24
x \= 4   ' same as: x = x \ 4   → x = 6  (integer division)
x ^= 2   ' same as: x = x ^ 2   → x = 36
x Mod= 5 ' VB 2026: x = x Mod 5 → x = 1

' Practical uses of Mod
Dim seconds As Integer = 137
Dim mins    = seconds \ 60       ' 2 minutes  (integer division)
Dim secs    = seconds Mod 60    ' 17 seconds (remainder)
lblTime.Text = $"{mins}m {secs}s" ' "2m 17s"

' Check even/odd with Mod
If n Mod 2 = 0 Then
    lblParity.Text = "Even"
Else
    lblParity.Text = "Odd"
End If

' Without parentheses — * evaluated before +
Dim result1 = 2 + 3 * 4          ' = 2 + 12 = 14  (NOT 20)

' With parentheses — force + first
Dim result2 = (2 + 3) * 4        ' = 5 * 4 = 20

' Exponentiation before multiplication
Dim result3 = 2 * 3 ^ 2          ' = 2 * 9 = 18  (^ first)
Dim result4 = (2 * 3) ^ 2        ' = 6 ^ 2 = 36

' Integer division and Mod together
Dim result5 = 17 \ 5 + 17 Mod 5  ' = 3 + 2 = 5  (\  before Mod before +)

' Complex formula — use parentheses for clarity
' Average of three values:
Dim avg = (a + b + c) / 3         ' ✔ parentheses ensure correct grouping
Dim bad = a + b + c / 3           ' ✘ only c is divided by 3!

' Quadratic discriminant: b²-4ac
Dim disc = b ^ 2 - 4 * a * c      ' ✔ correct by precedence rules

Const Pi As Double = Math.PI   ' use built-in constant for accuracy

' Areas
Dim areaCircle    = Pi * r ^ 2
Dim areaTriangle  = 0.5 * base * height
Dim areaRectangle = width * height
Dim areaTrapezoid = 0.5 * (a + b) * h

' Volumes
Dim volSphere     = (4 / 3) * Pi * r ^ 3
Dim volCylinder   = Pi * r ^ 2 * h
Dim volCone       = (1 / 3) * Pi * r ^ 2 * h
Dim volCube       = side ^ 3

' Display with 4 decimal places
lblArea.Text   = $"Circle area  (r={r}): {areaCircle:F4}"
lblVolume.Text = $"Sphere volume(r={r}): {volSphere:F4}"

' BMI = weight(kg) / height(m)²
Private Sub btnCalcBMI_Click(sender As Object, e As EventArgs) Handles btnCalcBMI.Click
    Dim weight, height As Double
    If Not Double.TryParse(txtWeight.Text, weight) OrElse
       Not Double.TryParse(txtHeight.Text, height) OrElse
       weight <= 0 OrElse height <= 0 Then
        lblBMI.Text = "⚠ Enter valid positive values."
        Return
    End If

    Dim bmi    = weight / (height ^ 2)
    Dim bmiR   = Math.Round(bmi, 1)

    Dim category As String
    Select Case bmiR
        Case Is < 18.5 : category = "Underweight"
        Case 18.5 To 24.9 : category = "Normal weight"
        Case 25.0 To 29.9 : category = "Overweight"
        Case Else         : category = "Obese"
    End Select

    lblBMI.Text = $"BMI: {bmiR:F1} — {category}"
End Sub

' A = P(1 + r/n)^(nt)
' P = principal, r = annual rate, n = compounds/year, t = years
Private Sub btnCalcCI_Click(sender As Object, e As EventArgs) Handles btnCalcCI.Click
    Dim principal As Decimal, rate As Double
    Dim n As Integer, years As Integer

    If Not Decimal.TryParse(txtPrincipal.Text, principal) OrElse
       Not Double.TryParse(txtRate.Text, rate) Then Return
    n     = CInt(cmbCompounding.SelectedIndex + 1)  ' 1=annual, 12=monthly
    years = CInt(txtYears.Text)

    Dim amount    = CDbl(principal) * Math.Pow(1 + rate / (100 * n), n * years)
    Dim interest  = amount - CDbl(principal)

    lblAmount.Text   = $"Final Amount:    {amount:C}"
    lblInterest.Text = $"Interest Earned: {interest:C}"
End Sub

' ── Legacy VB approach (still works) ──────────────────
Randomize()                                  ' seed with clock
Dim legacyRoll = Int(Rnd() * 6) + 1         ' 1 to 6 (die roll)

' ── Modern .NET 10 approach (recommended) ─────────────
Dim roll       = Random.Shared.Next(1, 7)    ' 1 to 6 (max is exclusive)
Dim percent    = Random.Shared.NextDouble() * 100  ' 0.0 to 99.999...
Dim coinFlip   = Random.Shared.Next(0, 2)    ' 0 or 1

' ── Practical: shuffle an array (Fisher-Yates) ────────
Dim cards() As Integer = Enumerable.Range(1, 52).ToArray()
For i = cards.Length - 1 To 1 Step -1
    Dim j   = Random.Shared.Next(0, i + 1)
    Dim tmp = cards(i) : cards(i) = cards(j) : cards(j) = tmp
Next

' ── Generate a random password ────────────────────────
Dim chars   = "ABCDEFGHJKLMNPQRSTUVWXYZabcdefghjkmnpqrstuvwxyz23456789!@#$"
Dim passLen = 12
Dim sb      = New System.Text.StringBuilder()
For i = 1 To passLen
    sb.Append(chars(Random.Shared.Next(0, chars.Length)))
Next
Dim password = sb.ToString()