POJ——1517

　　决定以后多练习算法，多上POJ，看过很多牛人都是这样成长起来的，也要像他们学习一下

　　先挑了题简单的，省得打击自己信心，后面自己写了一个随机数生成器，就按照随机出来的数选择吧

Description

A simple mathematical formula for e is 
e=Σ_0<=i<=n1/i!
where n is allowed to go to infinity. This can actually yield very accurate approximations of e using relatively small values of n.

Input

No input

Output

Output the approximations of e generated by the above formula for the values of n from 0 to 9. The beginning of your output should appear similar to that shown below.

Sample Input

no input

Sample Output

n e
- -----------
0 1
1 2
2 2.5
3 2.666666667
4 2.708333333
...

Accepted:

#include <iostream>
#include <iomanip>

using namespace std;
double Rank(int n);
int main()
{
    double e = 0;
    cout <<"n e"<< endl;
    cout <<"- -----------"<<endl;
    for(int i = 0; i <= 9; i++)
    {
        e += Rank(i);
        cout << i << " " <<setprecision(10)<< e <<endl;
    }
    return 0;
}
double Rank(int n)
{
    double val;
    double mul = 1;
    if(n == 0)
    {
        val = 1;
    }
    else
    {
        for(int i = 1;i <= n; i++)
        {
            mul *= i;
        }
        val = 1/mul;
    }
    return val;
}