Im trying to make a program which basically performs unit conversion.
I have basically made two text boxes, one for the S.I. Units and the other for British Units. The general idea is that when i input any number in the S.I. Unit text box, it should display the answer in British Unit text Box and similiarly if i input any number in British Unit Textbox, the answer should be displayed in S.I.Unit textbox. Now the problem lies here that the code that i created is by using if else. now the compiler automatically gives me the correct result in the British box when i input the value in the s.i. unit box, but when i input the value in the british text box, it gives an error that :
"An unhandled exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll

Additional information: Conversion from string "" to type 'Double' is not valid."

Heres the part of the code.

 Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        Dim p As String = "Pressure"
        Dim d As String = "Density"
        Dim t As String = "Temperature"
        Dim f As String = "Force"
        Dim si As Double = siubox.Text
        Dim pi As Double = bubox.Text
        Dim a As Double = 0.0208865 'for pressure si to british
        Dim b As Double = 47.73 'for pressure british to si
        While ComboBox1.Text = p
            If siubox.Text = si Then
                bubox.Text = a * si
            ElseIf bubox.Text = pi Then
                siubox.Text = pi * b

            End If
            Exit While

        End While

    End Sub

Will appreciate the help. Thanks.

Your if statement is wrong. siubox.text will always equal to si. Because you declare si to equal to siubox.text
so it will always calculate bubox.text=a * si

try an if statement of

if siubox.text<>"" then
bubox.text=a * si
siubox.text=pi * b
end if

Edited 4 Years Ago by ninjatalon

Thanks! That removed the error, but now, it shows the value of si unit 0 everytime i enter any british unit

oh i found the problem. lol i wrote the variable p instead of pi. Thanks alot :D

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