Построить таблицу значений по условию - VB

Option Explicit On
Option Strict On
Imports System.Math
 
Public Class Form5
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
 
        Dim x As Single
        Dim a As Single
        Dim b As Single
        Dim h As Single
        Dim n As Integer
        Dim y As Single
        Dim y1 As Single
 
        a = vvod(TextBox1)
        b = vvod(TextBox2)
        h = vvod(TextBox3)
        n = f_zikl(a, b, h)
        x = a
        y = f_y(x, y, y1)
        f_reg(n, x, h)
 
    End Sub
 
    Sub f_reg(ByVal n1 As Integer, ByVal x1 As Single, ByVal h1 As Single)
 
        Dim i As Integer
        Dim y As Single
        Dim z1 As String = "     N   | "
        Dim z2 As String = "     X   | "
        Dim z3 As String = "     Y   | "
        Dim z As String = "    "
        Dim z4 As String = "___________________"
 
        For i = 1 To n1
            z1 = z1 + Format(i, " 000") + Space(6) + "|" + Space(2)
            z2 = z2 + Format(x1, "0.000") + Space(3) + "|" + Space(2)
            z3 = z3 + Format(y, "0.000") + Space(3) + "|" + Space(2)
            x1 = x1 + h1
            z4 = z4 + "______________"
 
        Next i
 
        L_B_1.Items.Add(z4)
        L_B_1.Items.Add(z1)
        L_B_1.Items.Add(z4)
        L_B_1.Items.Add(z)
        L_B_1.Items.Add(z2)
        L_B_1.Items.Add(z4)
        L_B_1.Items.Add(z)
        L_B_1.Items.Add(z3)
        L_B_1.Items.Add(z4)
        L_B_1.Items.Add(z)
 
    End Sub
Private Function f_y(ByVal x As Single, ByVal y As Single, ByVal y1 As Single) As Integer
 
        If x > 1 Then
            y1 = CSng((Exp(x)))
            MsgBox(" расчет прошел по условию X > 1  ")
        ElseIf x < 0 Then
            y1 = (2 * x - 1)
            MsgBox(" расчет прошел по условию  X < 0 ")
        ElseIf x >= 0 And x <= 1 Then
            y1 = (-1)
            MsgBox(" расчет прошел по условию 0 ≤ x ≤ 1 ")
        End If
        Return CInt(y1)
    End Function
End Class