代码如下（仅供参考，有更好的程序欢迎沟通探讨）：
Private Sub Command1_Click()
'求循环节长度的程序，循环节必须大于5
Dim s As String
s = Text1
s1 = Mid(s, 1, 5)
For j = 6 To Len(s)
If s1 = Mid(s, j, 5) Then
s2 = 1
js = j
Exit For
End If
Next
If s2 = 1 Then
Text2 = "循环节长度" & js - 1 & " 循环节： “" & s1 & "……" & Mid(s, js - 1, 1) & "” "
Else
Text2 = "不循环"
End If
End Sub
Private Sub Command2_Click()
Text1 = ""
Text2 = ""
End Sub