编写自定义函数时，一般需要找到所需功能的核心算法，这个算法可先从一个特例开始进行编写。中心开花，逐步抽象，递次外延，直到获得满足功能需求的完整代码。下面以版友123xiaoniu同志昨日所问字符串排序问题为例，说明函数编写的过程。

第一步 先做字符串第一位的排序，基本思路为：将第一位的字符顺序向后逐个比较，取得最小值的字符，并将其排列到第一位。那么函数可写为：

Function orderStr(str As String) As String
Dim s As String
Dim j As Long
Dim n As Long
s = Mid(str, 1, 1)
For j = 1 To Len(str)
      If Mid(str, j, 1) < s Then s = Mid(str, j, 1): n = j '计算最小值及其位置。
Next
str = s & Replace(str, s, "", 1, 1) '排序
orderStr = str
End Function

第二步 做第一位到倒数第二位的循环比较排序。函数可写为：

Function orderStr(str As String) As String
Dim s As String
Dim i As Long, j As Long
Dim n As Long
For i = 1 To Len(str) - 1
    s = Mid(str, i, 1)
    For j = i + 1 To Len(str)
        If Mid(str, j, 1) < s Then s = Mid(str, j, 1): n = j
    Next
    str = Mid(str, 1, i - 1) & s & Replace(str, s, "", i, 1)
Next
orderStr = str
End Function

第三步 做可选择顺序和逆序的排序函数

Function orderStr(str As String, B As Long) As String
'功能：字符串排序
'参数：str--源字符串,B=1 降序 B=2 升序
Dim s As String
Dim i As Long, j As Long
Dim n As Long

For i = 1 To Len(str) - 1
    s = Mid(str, i, 1)
    For j = i + 1 To Len(str)
        Select Case B
            Case 1
                If Mid(str, j, 1) < s Then s = Mid(str, j, 1): n = j
            Case 2
                If Mid(str, j, 1) > s Then s = Mid(str, j, 1): n = j
        End Select
    Next
    str = Mid(str, 1, i - 1) & s & Replace(str, s, "", i, 1)
Next
orderStr = str
End Function

 点击下载此附件

 上一课   下一课