Как узнать, является ли данный четырехугольник параллелограммом

sub main
dim x(1to 4)as double
dim x(1to 4)as double
dim i as long
for i=1to 4
  x(i)=inputbox("Введите X" & i)
  y(i)=inputbox("Введите Y" & i)
next
if x(1)-x(2)=x(4)-x(3)and y(1)-y(2)=y(4)-y(3)then
  msgbox"Это параллелограм"
else
  msgbox"Это не параллелограм"
endif
end sub

Private Sub Command1_Click()
Sub main()
Dim x(1 To 4) As Double
Dim x(1 To 4) As Double
Dim i As Long
For i = 1 To 4
  x(i) = InputBox("Ââåäèòå X" & i)
  y(i) = InputBox("Ââåäèòå Y" & i)
Next
If x(1) - x(2) = x(4) - x(3) And y(1) - y(2) = y(4) - y(3) Then
  MsgBox "Ýòî ïàðàëëåëîãðàì"
Else
  MsgBox "Ýòî íå ïàðàëëåëîãðàì"
End If
End Sub

Private Sub Command1_Click()
'Sub main()
Dim x(1 To 4) As Double
Dim x(1 To 4) As Double
Dim i As Long
For i = 1 To 4
  x(i) = InputBox("Введите X" & i)
  y(i) = InputBox("Введите Y" & i)
Next
If x(1) - x(2) = x(4) - x(3) And y(1) - y(2) = y(4) - y(3) Then
  MsgBox "Это параллелограм"
Else
  MsgBox "Это не параллелограм"
End If
End Sub

4:   Dim y(1 To 4) As Double

Private Sub Command1_Click()
For i = 10 To 99
Next
Summa = Summa + i
Label1.Caption = "Summa  "
End Sub