Программа должна уметь распознавать функции, записанные в TextBox

For x = -10 To 10 Step 0.001
If Text1.Text <> "" Then Picture1.PSet (x, ?), vbRred
Next x

Private Sub Command1_Click()
Set objScript = CreateObject("MSScriptControl.ScriptControl")
objScript.Language = "VBScript"
For x = -10 To 10 Step 0.001
  If Text1.Text <> "" Then Picture1.PSet (x * 1000, 2000 + 1000 * objScript.eval(Replace(Text1.Text, "x", Str(x), , , vbTextCompare))), vbRred
Next x
End Sub

Stri$=Text1.Text

Private Sub Command1_Click()
Set objScript = CreateObject("MSScriptControl.ScriptControl")
objScript.Language = "VBScript"
On Error Resume Next
objScript.AddCode ("Function UserFunc(x)" & _
                "UserFunc = " & Text1.Text & _
                "End Function")
If Err Then MsgBox "Неверный синтаксис функции!": Exit Sub
For x = -10 To 10 Step 0.001
'    Debug.Print x, objScript.Run("UserFunc", x)
    Picture1.PSet (x * 1000, 2000 + 1000 * objScript.Run("UserFunc", x)), vbRred
Next x
End Sub

Option Compare Text
Option Explicit
Private Declare Function EbExecuteLine Lib "vba6.dll" (ByVal pStringToExec As Long, ByVal Foo1 As Long, ByVal Foo2 As Long, ByVal fCheckOnly As Long) As Long
 
 
Private Sub Command1_Click()
If Len(Text1.Text) <> 0 Then
Dim Result As Boolean, Code As String
Code = Text1.Text
Result = EbExecuteLine(StrPtr(Code), 0&, 0&, False) = 0
txtCode.SetFocus
End Sub

fun=text1.text
For x = -10 To 10 Step 0.001
If Text1.Text <> "" Then Picture1.PSet (x, fun), Str(Form2.Text1)
Next x

If Text1.Text <> "" Then Picture1.PSet (x, fun), Str(Form2.Text1)