Working with Controls

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    ' Convert text to numbers using Val() and add them
    Dim sum As Double = Val(TextBox1.Text) + Val(TextBox2.Text)

    ' Display the result in a message box
    MsgBox("The sum is " & sum)
End Sub

Private Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
    Dim n1, n2 As Double

    ' Modern VB 2026 approach: TryParse validates AND converts
    If Not Double.TryParse(txtNum1.Text, n1) OrElse Not Double.TryParse(txtNum2.Text, n2) Then
        lblResult.Text = "⚠ Please enter valid numbers"
        lblResult.ForeColor = Color.Red
        Return
    End If

    ' Calculate and display in label — no MsgBox needed
    Dim result As Double = n1 + n2
    lblResult.Text = result.ToString()
    lblResult.ForeColor = Color.DarkGreen
End Sub

Private Sub BtnVerify_Click(sender As Object, e As EventArgs) Handles BtnVerify.Click

    ' Step 1: Check the field is not empty
    If String.IsNullOrWhiteSpace(TxtAge.Text) Then
        LblResult.Text = "⚠ Please enter your age."
        LblResult.ForeColor = Color.OrangeRed
        Return
    End If

    ' Step 2: Check the value is a valid integer
    Dim age As Integer
    If Not Integer.TryParse(TxtAge.Text, age) Then
        LblResult.Text = "⚠ Please enter a whole number."
        LblResult.ForeColor = Color.Red
        Return
    End If

    ' Step 3: Validate realistic range
    If age < 0 Or age > 120 Then
        LblResult.Text = "⚠ Please enter a realistic age (0–120)."
        LblResult.ForeColor = Color.Red

    ElseIf age >= 18 Then
        LblResult.Text = "✔ Access granted. Welcome!"
        LblResult.ForeColor = Color.DarkGreen

    Else
        LblResult.Text = "✘ Access denied. Must be 18 or older."
        LblResult.ForeColor = Color.Crimson
    End If

End Sub

Private Sub BtnGreet_Click(sender As Object, e As EventArgs) Handles BtnGreet.Click

    If String.IsNullOrWhiteSpace(TxtName.Text) Then
        LblGreeting.Text = "Please enter your name first."
        LblGreeting.ForeColor = Color.OrangeRed
        Return
    End If

    ' Get current hour from system clock
    Dim currentTime As DateTime = DateTime.Now
    Dim hour As Integer = currentTime.Hour

    ' Determine time of day
    Dim timeOfDay As String
    If hour < 12 Then
        timeOfDay = "morning"
    ElseIf hour < 18 Then
        timeOfDay = "afternoon"
    Else
        timeOfDay = "evening"
    End If

    ' String interpolation — cleaner than using & repeatedly
    LblGreeting.Text = $"Good {timeOfDay}, {TxtName.Text}!"
    LblGreeting.ForeColor = Color.DarkBlue
    LblGreeting.Font = New Font(LblGreeting.Font, FontStyle.Bold)

    LblTime.Text = $"Current time: {currentTime:hh:mm tt}"

End Sub

Private Sub btnCalculate_Click(sender As Object, e As EventArgs) Handles btnCalculate.Click

    Dim weightKg, heightCm As Double

    If Not Double.TryParse(txtWeight.Text, weightKg) OrElse Not Double.TryParse(txtHeight.Text, heightCm) Then
        lblBMI.Text = "⚠ Enter valid weight and height."
        lblBMI.ForeColor = Color.OrangeRed
        Return
    End If

    If heightCm <= 0 OrElse weightKg <= 0 Then
        lblBMI.Text = "⚠ Values must be greater than zero."
        lblBMI.ForeColor = Color.OrangeRed
        Return
    End If

    ' BMI formula: weight(kg) / (height(m))^2
    Dim heightM As Double = heightCm / 100
    Dim bmi As Double = Math.Round(weightKg / (heightM * heightM), 1)

    ' Classify and colour-code using string interpolation
    Dim category As String
    If      bmi < 18.5 Then : category = "Underweight"  : lblBMI.ForeColor = Color.SteelBlue
    ElseIf  bmi < 25.0 Then : category = "Normal weight" : lblBMI.ForeColor = Color.DarkGreen
    ElseIf  bmi < 30.0 Then : category = "Overweight"    : lblBMI.ForeColor = Color.DarkOrange
    Else                  :   category = "Obese"         : lblBMI.ForeColor = Color.Crimson
    End If

    lblBMI.Text = $"BMI: {bmi} — {category}"
    lblBMI.Font = New Font(lblBMI.Font, FontStyle.Bold)

End Sub