做“1-（1/3）+(1/5)-(1/7)+(1/9)+……-（1/99）=”的结果
第一个算法：
Private Sub Command1_Click()
Dim sum#, i%, s%
sum = 0: s = 1
For i = 1 To 99 Step 2
sum = sum + (1 / i) * s
s = -s
Next i
MsgBox "结果为" & sum
End Sub
另一个算法是：
Private Sub Command1_Click()
Dim i As Integer, sum As Single
sum = 0
For i = 1 To 99 Step 2
sum = sum + (1 / i) * (-1) ^ (i + 1)
Next i
MsgBox "结果为" & sum
End Sub
