vb 统计字母出现的个数的函数

考试中碰到的，统计制定文本种子幕出现的次数，想破了脑也想不出是哪个函数，自定义一个也找不到头绪，请各位帮忙，不胜感激！
是统计出给定文本的每个字母（不去分大小写）并显示数量最多的那个字母，并显示个数

Private Sub Command1_Click()

Dim n As Integer
Dim i As Integer
Dim one As Integer
n = 0
For i = 1 To Len(Text1.Text)
one = Asc(Mid(Text1.Text, i, 1))
If (one >= 65 And one <= 90) Or (one >= 97 And one <= 122) Then n = n + 1
Next i
MsgBox "共有" & n & "个字母。"
End Sub

　　在“通用声明”代码区声明(窗体)模块级变量
Option Explicit

Dim letters As Integer '声明模块级变量，此变量计算字母个数
Dim space As Integer '空格个数
Dim digit As Integer '数字个数
Dim others As Integer '其他字符个数

输入cmdStat_Click()事件过程代码
Private Sub cmdStat_Click()
Dim InputStr As String '局部变量，此变量存储输入的字符串
Dim i As Integer '循环控制变量，整型
Dim CaseStr As String '此变量保存储所截取的字符
letters = 0 '初始化为0
space = 0
digit = 0
others = 0

InputStr = txtInput.Text '取得输入的字符串
For i = 1 To Len(InputStr) '开始分别统计个数
CaseStr = Mid(InputStr, i, 1) '取得某个字符