这是一个判断输入的字符串有大写字母多少个，小写字母多少个，数字字符多少个，其它字符多少个的代码，是我看的教材上的，我不太明白，请那位大虾给逐句注释一下，不胜感谢！

dim a(4) as integer,ch as srting,instring as integer
dim i as integer
dim srt as string()={"大写字母","小写字母","数字字符","其它字符"}
instring=txtinput.text
for i=0 to instring.length-1
ch=instring.chars(i)
select case ch
case "A"to"Z"
a(0)=a(0)+1
case "a"to"z"
a(1)=a(1)+1
case "0"to"9"
a(2)=a(2)+1
case else
a(3)=a(3)+1
end select
next i
for i=0 to 3
txtoutput.text +=srt(i)+a(i).tostring+vbcrlf
next

Dim a(4) As Integer, ch As String, instring As String
Dim i As Integer
Dim srt As String() = {"大写字母", "小写字母", "数字字符", "其它字符"}
instring = TextBox2.Text
For i = 0 To instring.ToString.Length - 1
ch = instring.ToString.Chars(i)
Select Case ch
Case "A" To "Z"
'计算大写字母个数
a(0) = a(0) + 1
Case "a" To "z"
'计算小写字母个数
a(1) = a(1) + 1
Case "0" To "9"
'计算数字个数
a(2) = a(2) + 1
Case Else
'计算其他个数
a(3) = a(3) + 1
End Select
Next i
For i = 0 To 3
TextBox2.Text += srt(i) + a(i).ToString + vbCrLf
Next
这样才是对的，自己设置断点跟踪下，就明白了

谢谢梓风，有几句不明白，请指点一二，谢谢！
Dim srt As String() = {"大写字母", "小写字母", "数字字符", "其它字符"}
instring = TextBox2.Text
For i = 0 To instring.ToString.Length - 1
ch = instring.ToString.Chars(i)
这几句不太明白啊！

Dim srt As String() = {"大写字母", "小写字母", "数字字符", "其它字符"}
定义一个string类型的数组
instring = TextBox2.Text
获取TextBox2文本的值
For i = 0 To instring.ToString.Length - 1
ch = instring.ToString.Chars(i)
遍历赋值给ch

多谢梓风的指点，我还是不太明白 a(0) = a(0) + 1以及后面类似的几句的意思，请您指点啊，谢谢！

统计对应的{"大写字母", "小写字母", "数字字符", "其它字符"}中的个数的