Private Sub Command1_Click()
number = InputBox("請入一個數", "檢查質數")
number = Val(number)
check_num = check(number)
Select Case check_num
Case 1
MsgBox "是質數"
Case 2
MsgBox "不是質數"
num (number)
Case 3
MsgBox "無意義"
End Select
Exit Sub
End Sub


Public Function check(ByVal Number As Integer)
If Number <= 1 Then
check_num = 3
Else
If Number = 2 Then
check_num = 1
Else
check_num = 1
For i = 2 To Number / 2
If Number Mod i = 0 Then
check_num = 2
End If
Next i
End If
End If
check = check_num
End Function

Public Function num(ByVal number As Integer)
For i = 2 To number
If number Mod i = 0 Then
MsgBox i
End If
Next i
End Function

稍微修改了一下你的程式..
希望這對你有用
PS.剛剛已經貼在七嘴八舌版了-_-||