如何從c#中的方法中的for語句返回值

Question

我不明白為什么這段代碼不能在階乘方法中返回result 。 任何幫助，將不勝感激。

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

namespace CalculatorProgram
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("What is the first number:\n> ");
            decimal x = Convert.ToDecimal(Console.ReadLine());

            Console.Write("What is the second integer:\n> ");
            decimal y = Convert.ToDecimal(Console.ReadLine());

            Console.Write("What is the operation that you would like to use? 
Enter + , - , * , / , or ! :\n> ");
            string operation = Console.ReadLine();

            if (operation == "!")
            {
                Console.Write("Which number would you like to use?\n> ");
                int num = int.Parse(Console.ReadLine());
                Console.WriteLine("{0}! = {1}", num, Factorial(num));
            }
        }

        private static int Factorial(int a)
        {
            int result;
            for (int i = 1; i < a + 1; i++ )
            {
                result = a * i;
            }
            return result;
        }
    }
}

Answer 1

result = a * i; 是不正確的。

它應該類似於result = result * i; , result初始化為 1：即更改int result; 到int result = 1; .

目前您正在評估a * a 。

Answer 2

試試這個：

private static int Factorial(int a)
{
    int result = 1;
    for (int i = 2; i < a + 1; i++)
    {
        result = result * i;
    }

    return result;
}