Factorial Calculate

Public Sub validation()
        If txtFirstNum.Text = "" Then
            MsgBox("First Number is Empty")
        ElseIf Not IsNumeric(txtFirstNum.Text) Then
            MsgBox("First Number is not numeric")
        Else
            call factorial
        endif
endsub

Public Sub factorial()
        Dim counter As Integer
        Dim result As Long
        Dim x As String = (Val(txtFirstNum.Text))
        counter = 1
        result = 1
        While counter <= x
            result = result * counter
 
            counter = counter + 1
 
            txtAnswer.Text = result
        End While
    End Sub

Private sub cmdcalculate_click(.)
call validation
endsub

    Private Function Factorial(ByVal Num As Int64) As Int64
        Factorial = 1
        For i = 2 To Num
            Factorial *= Num
        Next
    End Function

    Private Function Factorial(ByVal Num As UInt64) As UInt64
        Dim i As UInt64
        Factorial = 1
        For i = 2 To Num
            Factorial *= Num
        Next
    End Function

Private Function Factorial2(ByVal Num As Int64) As Int64
 
        If Num <= 1 Then
            Return 1
        Else
            Return Num * Factorial2(Num - 1)
        End If
 
    End Function

Public Class frmFactorialCalculator
 
    Private Sub btnCalFactorial_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalFactorial.Click
	        Dim intNumber As Integer = 0
	        Dim IntFactorial As Integer = 0
	        Try
	            intNumber = Val(txtNumber.Text.Trim)
	            IntFactorial = fnGetFactorial(intNumber)
	            lblresult.Text = IntFactorial
	        Catch ex As Exception
	            MessageBox.Show(ex.Message)
	        End Try
	    End Sub
 
	    'Factorial Function Codes
	    Private Function fnGetFactorial(ByVal num As Integer) As Integer
	        Dim intfac As Integer = 1
	        Dim i As Integer
 
	        For i = 2 To num
	            intfac *= i
	        Next
	        fnGetFactorial = intfac
	    End Function
 
	End Class