Public Function DEC_to_BIN(Dec As Long) As String
DEC_to_BIN = ""
Do While Dec > 0
DEC_to_BIN = Dec Mod 2 & DEC_to_BIN
Dec = Dec \ 2
Loop
End Function


Private Sub Command5_Click(）这样调用不对
Dim d As String
 DEC_to_BIN(d) = 8
d = Text1.Text
End Sub

这函数能多次调用吗？谢谢大家

试试：
Public Function DEC_to_BIN(Dec As Long) As String
DEC_to_BIN = ""
Do While Dec > 0
DEC_to_BIN = Dec Mod 2 & DEC_to_BIN
Dec = Dec \ 2
Loop
End Function


Private Sub Command5_Click(）这样调用不对
Dim d As String
 d=DEC_to_BIN(8)
 Text1.Text=d
End Sub