C# 计算C中的阶乘#

我正试图编写一个程序，将用户的输入值，并询问他们是否要计算数字1到n的值或n的阶乘！ 这就是我目前所拥有的

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Project_2_Part_B
{
    class Program
    {
        static void Main(string[] args)
        {
            var Fkeylow = "f";
            var FkeyCap = "F";
            var Skeylow="s";
            var SkeyCap="S";
            int n = 0;
            long factorial = n;

            Console.WriteLine("Input a value n");
            n = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine("Do you want to calculate factorial or sum");
            Console.WriteLine("Enter F or S");

            var A = Console.ReadLine();

            if (A == Fkeylow)
                Console.WriteLine();

            if (A == FkeyCap)
                Console.WriteLine();

            var B=Console.ReadLine();

            if (B == Skeylow)
                Console.WriteLine();

            if (B == SkeyCap)
                Console.WriteLine();

            Console.WriteLine("Press any key to close...");
            Console.ReadLine();
        }
    }
}

---

我的问题是计算语法，使代码在n>1时执行n*（n-1）。

使用递归是另一种方法：

static void Main(string[] args)
{
    Console.WriteLine("Input a value n");
    string number = Console.ReadLine(); // Read number
    int n = Convert.ToInt32(number); // Converting to int

    Console.WriteLine("Do you want to calculate factorial or sum? ");
    Console.WriteLine("Enter F or S. ");
    string choose = Console.ReadLine(); // F or S

    int result = -1; // To view later

    if (choose == "f" || choose == "F")
    {
        result = 1;
        for (int i = n; i >= 1; i--) // Loop for calculating factorial
            result *= i;
    }
    else if (choose == "s" || choose == "S")
    {
        result = 0;
        for (int i = n; i >= 1; i--) // Loop for calculating sum
            result += i;
    }

    Console.WriteLine(result); // Printing answer

    Console.WriteLine("Press any key to close...");
    Console.ReadLine();
}

 static void Main(string[] args)
 {
        int n = 5;
        Console.WriteLine(factorial(n));
        Console.WriteLine(sum(n));
        Console.Read();
 }

 public static int sum(int n)
 {
     if(n==0)
        return 0;
     return n+sum(n-1);
 }
 public static int factorial(int n)
 {
    if (n == 1)
       return 1;
    return n * factorial(n - 1);
 }

印刷品：

120 -->5!
15  -->1+2+3+4+5

---

基本解决方案在这里，经过测试

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication50
{
    class Program
    {
        static void Main(string[] args)
        {
            NumberManipulator manipulator = new NumberManipulator();
            Console.WriteLine("Factorial of six is :" + manipulator.factorial(16));
            Console.ReadLine();
        }
    }
class NumberManipulator
{
    public int factorial(int num)
    {
        int result=1;
        int b = 1;
        do
        {
            result = result * b;//fact has the value 1  as constant and fact into b will be save in fact to multiply again. 
            Console.WriteLine(result);
            b++;
        } while (num >= b);
        return result;
    }
  }
}

---

@斯蒂芬：你的意思是：输入=10->打印10！然后是9！然后。。。1.与用户输入5一样，按下“f”表示阶乘，输出应为120。（5×4×3×2×1）@lcarus他看起来像乞丐，无法理解solution@Mr.DDD好了，他不喜欢递归版本。太遗憾了：’（我很确定“项目2\u Part\u B”是作为初学者的赠品。；）我总是把事情复杂化。非常感谢你的帮助！