vb编程 计算f=1-1/(2*3)+1/(3*4)-1/(4*5)+……+1/(19*20)

1、sign = -1
2、for i=2 to 19
3、sign = -sign
给分吧。。
运行结果是0.8875428

Private Sub Form_Click()
'计算f=1-1/(2*3)+1/(3*4)-1/(4*5)+……+1/(19*20)
Dim f As Single
Dim i As Integer
Dim sign As Integer
sign=-1'-----1------
f = 1
for i=2 to 19 '-----2------
f = f + sign / (i * (i + 1))
sign=sign*(-1) '------3-------
Next i
Form1.Print "f="; f
End Sub

1.for i=1 to 19
if i=1 then

2. else

3.end if

1、sign = -1
2、for i=2 to 19
3、sign = -sign
=0.8875428