Ytukyg

I keep receiving the error mention in the title. I've tried replacing all "+" with "&" as mentioned in other threads, but it doesn't seem to work. I wanted to create a program that allows me to see my weight on other planets using VB.net but I cannot get past this "Input string was not in a correct format" error. Any help please? The error occurs at the first line.

                    Convert.ToDouble(ComboBox1.SelectedItem())

    If ComboBox1.SelectedItem = 0 Then

        Label4.Text = "Your weight on " + ComboBox1.SelectedItem() + " is " + (TextBox1.Text * 0.378)

    ElseIf ComboBox1.SelectedItem = 1 Then

        Label4.Text = "Your weight on " + ComboBox1.SelectedItem() + " is " + (TextBox1.Text * 0.905)

    ElseIf ComboBox1.SelectedItem = 2 Then

        Label4.Text = "Your weight on " + ComboBox1.SelectedItem() + " is " + (TextBox1.Text * 1.0)

    ElseIf ComboBox1.SelectedItem = 3 Then

        Label4.Text = "Your weight on " + ComboBox1.SelectedItem() + " is " + (TextBox1.Text * 0.379)

    ElseIf ComboBox1.SelectedItem = 4 Then

        Label4.Text = "Your weight on " + ComboBox1.SelectedItem() + " is " + (TextBox1.Text * 2.529)

    ElseIf ComboBox1.SelectedItem = 5 Then

        Label4.Text = "Your weight on " + ComboBox1.SelectedItem() + " is " + (TextBox1.Text * 1.066)

    ElseIf ComboBox1.SelectedItem = 6 Then

        Label4.Text = "Your weight on " + ComboBox1.SelectedItem() + " is " + (TextBox1.Text * 0.903)

    ElseIf ComboBox1.SelectedItem = 7 Then

        Label4.Text = "Your weight on " + ComboBox1.SelectedItem() + " is " + (TextBox1.Text * 1.096)

    ElseIf ComboBox1.SelectedItem = 8 Then

        Label4.Text = "Your weight on " + ComboBox1.SelectedItem() + " is " + (TextBox1.Text * 0.069)

    End If

Thank you all for your help! I solved the problem, by adding CDbl() just before the user input, used Option Strict On, and used SelectedIndex() instead of SelectedItem().

Here is the code:

If ComboBox1.SelectedIndex = 0 Then

        Label4.Text = "Your weight on Mercury" & " is " & (CDbl(TextBox1.Text) * 0.378)

    ElseIf ComboBox1.SelectedIndex = 1 Then

        Label4.Text = "Your weight on Venus" & " is " & (CDbl(TextBox1.Text) * 0.905)

    ElseIf ComboBox1.SelectedIndex = 2 Then

        Label4.Text = "Your weight on Earth" & " is " & (CDbl(TextBox1.Text) * 1.0)

    ElseIf ComboBox1.SelectedIndex = 3 Then

        Label4.Text = "Your weight on Mars" & " is " & (CDbl(TextBox1.Text) * 0.379)

    ElseIf ComboBox1.SelectedIndex = 4 Then

        Label4.Text = "Your weight on Jupiter" & " is " & (CDbl(TextBox1.Text) * 2.529)

    ElseIf ComboBox1.SelectedIndex = 5 Then

        Label4.Text = "Your weight on Saturn" & " is " & (CDbl(TextBox1.Text) * 1.066)

    ElseIf ComboBox1.SelectedIndex = 6 Then

        Label4.Text = "Your weight on Uranus" & " is " & (CDbl(TextBox1.Text) * 0.903)

    ElseIf ComboBox1.SelectedIndex = 7 Then

        Label4.Text = "Your weight on Neptune" & " is " & (CDbl(TextBox1.Text) * 1.096)

    ElseIf ComboBox1.SelectedIndex = 8 Then

        Label4.Text = "Your weight on Pluto" & " is " & (CDbl(TextBox1.Text) * 0.069)

    End If

Use data-binding instead of If else

and Double.TryParse instead of CDbl for conversions from string to integers

and & instead of + when combining strings(or String interpolation).

Option Strict On - always (which you already did)

Public Class Planet

    Public ReadOnly Property Name As String

    Public ReadOnly Property WeightFactor As Double 



    Public Sub New(name As String, weightFactor As Double)

        Me.Name = name 

        Me.WeightFactor = weightFactor

    End Sub     

End Class



' Create planets and bind it to the ComboBox

' Form constructor

Public Sub New()

    InitializeComponent()



    Dim planets As New List(Of Planet) From

    {

        New Planet("Mercury", 0.378),

        New Planet("Venus", 0.905),

        New Planet("Earth", 1.0),

        New Planet("Mars", 0.379),

    }



    ' Bind planets to combobox

    ComboBox1.DisplayMember = "Name" ' Name of the property used for displaying text

    ComboBox1.ValueMember = "WeightFactor" ' Name of the property used as selected value

    ComboBox1.DataSource = planets

End Sub

Then your calculation code will look simpler

Dim personWeight AS Double

If Double.TryParse(textbox1.Text, personWeight) Then

    ' SelectedItem is instance of selected planet

    Dim planet = DirectCast(ComboBox1.SelectedItem, Planet)



    Dim weightOnPlanet = personWeight * planet.WeightFactor

    Label4.Text = $"Your weight on {planet.Name} is {weightOnPlanet}"

End If