【例】分别按以下要求求ex≈1+(x/1!)+(x2/2!)+(x3/3!)+…+(xn/n!)
1）直到第20项。
2）直到最后一项小于10-6。
X的值由输入框输入。
程序源码一（计算分数序列的前20项累加和）：
Option Explicit
Private Sub Form_Click()
Dim I As Integer, IJC As Double, J As Integer, X As Integer, Sum As Double
Sum = 1
X = Val(InputBox("请输入X的值："))
For I = 1 To 19
IJC = 1
For J = 1 To I ' 计算分母I的阶乘
IJC = IJC * J
Next J
Sum = Sum + (X ^ I) / IJC
Next I
Print Sum
End Sub
程序源码二：
分析：用I表示分母1，2，3…
用IJC表示1!，2!，3!…
用Term表示每一项的值，则Term=xI/IJC
用Sum表示累加和
循环初始条件：I=1，Sum=1
循环终止条件：Term<0.000001
Option Explicit
Private Sub Form_Click()
Dim IJC As Double, Sum As Double, Term As Double
Dim I As Integer, J As Integer, X As Integer
Sum = 1: I = 1
X = Val(InputBox("请输入X的值："))
Do
IJC = 1
For J = 1 To I ' 计算分母I的阶乘
IJC = IJC * J
Next J
Term = (X ^ I) / IJC
Sum = Sum + Term
I = I + 1
Loop Until Term < 0.000001
Print Sum
End Sub