Button on click event disable button after 5 times it was clicked - asp.net

Question

I am fairly new to VB.NET. I feel like I did the hard parts and struggling with the easy one! I googled it before coming here but still struggling.
Basically I have a drop down list with all the available treatments and button next to it ( Add treatment). Every time I choose treatment from list I click on the button and it add it then bind it to gridview, the only issue is I want users to be able to add up to 5 treatments then disable the button. The question how Can I say find the number of times the button was clicked then I suppose I can just put If statement, I dont know how to find the value of the number of times the button was clicked.
Dim availableTreatment As ListItem = New ListItem
Dim count As Integer = 0
For count = 0 To 4
If count <= 4 And btnavailableTreatment ( button clicked value is what should go here) Then
availableTreatment = DDTreatmentList.SelectedItem
c.name = availableTreatment.Value
saveTreatment(c)
gvavailableTreatment.DataSource = getTreatment(c.name)
gvavailableTreatment.DataBind()
Else
btnavailableTreatment.Enabled = False
End If
count = count + 1
Next

Answer 1

Add this markup to your page:
<asp:HiddenField id="NumberOfTimesClickedHiddenField"
value="0"
runat="server"/>
Add this to your button click handler
'get previous value
Dim numberOfTimesClicked = Integer.Parse(NumberOfTimesClickedHiddenField.Value)
'increment value
numberOfTimesClicked += 1
'store new value
NumberOfTimesClickedHiddenField.Value = numberOfTimesClicked.ToString()
If numberOfTimesClicked >= 5 Then
btnavailableTreatment.Enabled = False
End If
Now the value will be persisted in the form data on the page.
I originally wrote this in C#, and I'm not a VB.NET programmer so I used a translator to convert it. There may be syntax errors but the general flow should be correct.