ตอนนี้หาค่า factorial ได้ทุกลูปแล้ว เหลือแค่ Do Loop unit ช่วยดูให้หน่อยนะค่ะว่ามันผิดตรงไหน แต่loop อื่นได้หมดแล้ว

Public Class Form2

    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ListBox1.Items.Add("For Next")
        ListBox1.Items.Add("Do While Loob")
        ListBox1.Items.Add("Do Loob Until")
        ListBox1.Items.Add("Do Loob While")
    End Sub
    Sub Result()
        Dim a As Int32
        Dim fac As Int32 = 1
        Dim i As Int32
        a = Val(TextBox1.Text)
        For i = a To 1 Step -1
            fac = fac * i
        Next
        Label5.Text = fac
    End Sub
    Sub Resule1()
        Dim a1 As Int32
        Dim fac1 As Int32 = 1
        Dim i1 As Int32 = 1
        a1 = Val(TextBox1.Text)

        Do While a1 >= i1
            fac1 = fac1 * i1
            i1 = i1 + 1
        Loop
        Label5.Text = fac1
    End Sub
    Sub Resule2()
        Dim a2 As Int32
        Dim fac2 As Int32 = 1
        Dim i2 As Int32 = 1
        a2 = Val(TextBox1.Text)
        Do
            fac2 = a2 * i2

            i2 = i2 + 1

        Loop Until a2 >= i2
        Label5.Text = fac2

    End Sub
    Sub Resule3()

        Dim i3 As Integer = 1
        Dim a3 As Integer
        Dim fac3 As Integer = 1
        a3 = Val(TextBox1.Text)
        Do

            fac3 = fac3 * i3
            i3 = i3 + 1

        Loop While a3 >= i3

        Label5.Text = fac3


       
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If ListBox1.Text = "For Next" Then
            Call Result()
        ElseIf ListBox1.Text = "Do While Loob" Then
            Call Resule1()
        ElseIf ListBox1.Text = "Do Loob Until" Then
            Call Resule2()
        ElseIf ListBox1.Text = "Do Loob While" Then
            Call Resule3()
        End If
    End Sub

    Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged

    End Sub
End Class