如何用函数调用实现，不要复杂的？

根据给定公式计算e的值：1+1/1!+1/2!+1/3!+……+1/n!的值（取前n项)，要求在主函数中输入n的值，调用函数并输出结果。

C++版本

#include<iostream>
using namespace std;
double f(int n){
    if(n == 0 || n == 1) return 1.0;
    else return f(n - 1) * n;
}
 
int main(){
    int N;
    cin >> N;
    double s = 0;
    int i;
    for(i = 0; i <= N; ++i)
        s += 1.0 / f(i);
    cout << s << endl;
    return 0;
}

C版本

#include <stdio.h>
double f(int n){
    if(n == 0 || n == 1) return 1.0;
    else return f(n - 1) * n;
}
 
int main(){
    int N;
    scanf("%d", &N);
    double s = 0;
    int i;
    for(i = 0; i <= N; ++i)
        s += 1.0 / f(i);
    printf("%lf",s);
    return 0;
}

#include<iostream>
using namespace std;
double factorial(int k)
{
    if (k == 1)
    {
        return 1;
    }
    else
    {
        return k * factorial(k - 1);
    }
}
int main()
{
    double e = 1;
    int n;
    cout << "请输入n的值：";
    cin >> n;
    for (int i = 1; i <= x; i++)
    {
        e = e + 1.0/ factorial(i);
    }
    cout << fixed <<e << endl;
    return 0;
}