I'm having a small problem with my calculator. I can't seem to find the answer for my question. Somebody help
When I press add,sub, mul, div, button the number disappears.
I want to be able to get the number to stay there when I press the + button but it disappears.

Another problem is when I press equals, I get the right number. But when I put in another number it continues with my previous answer. I have a clear button but I don't want them to have to press. I want to be able to clear the answer and put another number without having to press the clear button.

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Here's my code:

Public Class Calculator
Inherits System.Windows.Forms.Form

Private Calc As Boolean = False
Private num1, num2 As Double
Private number As String
Private answer As Double

'Number Buttons from 0-9
Private Sub num1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn1.Click, btn2.Click, btn3.Click, btn4.Click, btn5.Click, btn6.Click, btn7.Click, btn8.Click, btn9.Click, btn10.Click
If (Calc Or (txt1.Text = "0")) Then
txt1.Text = ""
End If
txt1.Text = txt1.Text + CType(sender, Button).Text
Calc = False
End Sub

'The Math Functions (+, -, *, /)
Private Sub btnadd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnadd.Click
num1 = Val(txt1.Text)
number = "+"
txt1.Text = ""

End Sub

Private Sub btnsub_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnsub.Click
num1 = Val(txt1.Text)
number = "-"
txt1.Text = ""

End Sub

Private Sub btnast_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnast.Click
num1 = Val(txt1.Text)
number = "*"
txt1.Text = " "
End Sub

Private Sub btndiv_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btndiv.Click
num1 = Val(txt1.Text)
number = "/"
txt1.Text = " "
End Sub

'The Equal Function (=)
Private Overloads Sub btnequal_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnequal.Click
num2 = Val(txt1.Text)
If number = "+" Then answer = num1 + num2
If number = "-" Then answer = num1 - num2
If number = "*" Then answer = num1 * num2
If number = "/" Then answer = num1 / num2
txt1.Text = answer 'Displays the answer in the TextBox


End Sub

Private Sub btnclear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnclear.Click
txt1.Clear() 'Clears the numbers in the TextBox
End Sub


End Class