小程序（求N个数的阶乘）

using System;public class Factorial{

public long factorial(long x){

return ((x<=1) ? 1 : x*(factorial(x-1)));

}

}

public class FactorialSum

{

public static void Main()

{

long temp=0;

long sum=0;

Console.WriteLine ("输入一个数:");

int x=int.Parse (Console.ReadLine ());

for(int i=1;i<=x;i++)

{

Factorial f1=new Factorial ();

temp+=f1.factorial (i);

}

sum+=temp;

Console.WriteLine ("1!+2!+3!+...+a!="+sum);

}}