Visual Basic : Sayı Tekmi Çift mi

Private Sub Command1_Click()
Dim a As Long
If Text1.Text = "" Then
MsgBox ("Boş Sayı Girilmez"), vbCritical, "HATA"
ElseIf a >= 0 Then
MsgBox ("POZİTİF"), vbInformation, "POZİTİF"
Else
MsgBox ("NEGATİF"), vbInformation, "NEGATİF"
End If
End Sub

Private Sub Command2_Click()
If Text1.Text = "" Then
MsgBox ("Boş Sayı Girilmez"), vbCritical, "HATA"
ElseIf Text1.Text Mod 2 = 0 Then
MsgBox ("ÇİFT"), vbInformation, "ÇİFT"
Else
MsgBox ("TEK"), vbInformation, "TEK"
End If
End Sub

Private Sub Command3_Click()
Text1.Text = Clear
End Sub

Private Sub Command4_Click()
End
End Sub