How do i get my sqrt button and percentage button to work on my calculator

[RoxyBeginner]

I got every other operation button to work besides sqrt, and percentage. I've done the same thing for addition, subtraction, etc. and it doesn't seem to work.

here's my globals

Public Class Form1

    Private first As Double
    Private second As Double
    Private oper As String
    Private negpos As Boolean

Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
        first = txtoutput.Text
        txtoutput.Clear()
        oper = "+"

    End Sub

    Private Sub btnEqual_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnEqual.Click
        second = txtoutput.Text
        If (oper = "+") Then
            txtoutput.Text = first + second
        Else
            If (oper = "-") Then
                txtoutput.Text = first - second
            Else
                If (oper = "*") Then
                    txtoutput.Text = first * second
                Else
                    If (oper = "/") Then
                        txtoutput.Text = first / second
                    Else
                        If (oper = "s") Then
                            txtoutput.Text = System.Math.Sqrt(first)
                        Else
                            If (oper = "%") Then
                                txtoutput.Text = (first * second) / 100
                            End If
                        End If
                    End If
                End If
            End If
        End If
    End Sub

    Private Sub btnSubstract_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSubstract.Click
        first = txtoutput.Text
        txtoutput.Clear()
        oper = "-"
    End Sub

    Private Sub btnMultiply_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnMultiply.Click
        first = txtoutput.Text
        txtoutput.Clear()
        oper = "*"
    End Sub

    Private Sub btnDivide_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDivide.Click
        first = txtoutput.Text
        txtoutput.Clear()
        oper = "/"
    End Sub

    Private Sub btnSqrt_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSqrt.Click
        first = txtoutput.Text
        txtoutput.Clear()
        oper = "s"
    End Sub

    Private Sub btnPercent_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPercent.Click
        first = txtoutput.Text
        oper = "%"
    End Sub
End Class

[Joseph Martell]

First, what exactly is going wrong? How are your square root and percent functions not working correctly? Are exceptions being thrown or are the results just off?

Second, and this is mostly a question of personal preference and not functionality, you could use a select case statement instead of all of those nested if's. It would be functionally the same as your current code, but it might be easier to read.

[!NoItAll]

Yeah - I'm going with Joseph. A Select Case section would be a much better way to handle this.
As far as assigning the output of your calculations to the text control you should also make sure you are assigning a string.
Some quick examples of how to do this...

txtoutput.Text = (first - second).ToString
txtoutput.Text = System.Math.Sqrt(first).ToString

VB will do the conversion for you - but it's bad form.