Public Class Form1
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim no As Integer
no = Val(TextBox1.Text)
fact(no)
Dim ans As Integer = 0
End Sub
Function fact(ByVal no As Integer) As Integer
If no > 0 Then
ans = ans + (no * fact(no - 1))
TextBox2.Text = ans
End If
End Function
End Class
You need to account for all cases. Your function does nothing for Fact(0). You should also just return a value rather than assign it to the textbox in the function.
Private Function Fact(no As Integer) As Integer
If no > 1 Then
Return no * Fact(no - 1)
Else
Return 1
End If
End Function
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