谁能帮我设计这个简单的算法

思路:先偶数累乘,再分数累加
Dim y As Double, n As Integer, i As Integer
Dim s As Long
s = 1
n = Val(InputBox("输入一数字"))
For i = 1 To n
s = s * (2 * i)
y = y + 1 / s
Next i
Print y

Dim sum, sum1, sum2 As Integer
Dim sum3 As Long
sum = 0
sum1 = 1
For i = 1 To 3 '这个是n
sum1 = sum1 * i
sum2 = 1
For j = 1 To i
sum2 = sum2 * j
Next j
sum3 = 2 ^ (j - 1) * sum2
sum = sum + 1 / sum3
Next i
Text1.Text = sum '最后把结果送到text1中

#include "stdio.h"
main()
{
int n,i;
float Asum=1,Bsum=0;
scanf("%d",&n);
for(i=1;i<=n;i++)
{
Asum=Asum/(2*i);
Bsum+=Asum;
}
printf("%f\n",Bsum);
}
算法大概是这样的:
先获取每一项的值,它的第二项就是它的(2*i)分之一,Bsum把所有的项累加起来就得了.