LZ的三个简单问题代码如下，未详细设计，仅供参考：
具体是在工程的form1窗体中添加三个命令按钮，其它属性默认即可，将下面的代码拷贝过去并运行即可。
Private Sub Command1_Click(Index As Integer)
    '输出1-1/2+1/3-1/4+。
  。。
  +1/99-1/100 的和
    Dim i As Double
    Dim sum As Double
    sum = 0    
    For i = 1 To 100
        If i Mod 2 Then
            sum = sum + 1 / i
        Else
            sum = sum - 1 / i
        End If
    Next
    MsgBox sum
End Sub
Private Sub Command2_Click()
    Dim val As String
    val = InputBox("请输入一个整数:", "判断是否素数")
    If val = "" Then Exit Sub
    MsgBox analyse(CLng(val)) 
End Sub
Function analyse(val As Long)
    Dim i As Long
    For i = 2 To val - 1
        If val Mod i = 0 Then
            analyse = 0
            Exit Function
        End If
    Next
    analyse = 1
End Function
Private Sub Command3_Click()
    Dim str As String, temp As String
    Dim p As Long, i As Long, j As Long, k As Long
    i = 0
    j = 0
    k = 0
    
    str = InputBox("请输入一个字符串:", "统计分析串")
    If str = "" Then Exit Sub    
    For i = 1 To Len(str)
        temp = Mid(str, i, 1)
        If IsNumeric(temp) Then
            i = i + 1
        ElseIf (Asc(temp) >= Asc("A") And Asc(temp) = Asc("a") And Asc(temp) <= Asc("z")) Then
            j = j + 1
        Else
            k = k + 1
        End If
    Next
    MsgBox "数字：" & CStr(i) & " 字母：" & CStr(j) & "其它：" & CStr(k) '输出统计结果
    MsgBox StrReverse(str)  '反序输出    
End Sub
。