用函数做 ：判断质数、与7相关的数、阶乘、一元二次方程

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

namespace 函数
{
    class Program
    {
        /// <summary>
        /// 判断质数
        /// </summary>
        /// <param name="a"></param>
        public void pdsbszs(int a)
        {
            int sum = 0;
            for (int i = 1; i <= a; i++)
            {
                int b = a % i;
                
                if (b == 0)
                {
                    sum++;                  
                }
            }
             if (sum == 2)
            {
                Console.Write("这是个质数");
            }
            else
             {
                 Console.Write("这不是个质数");
             }
            
        }
        /// <summary>
        /// 与7相关的数
        /// </summary>
        /// <param name="s"></param>
       public void y7(string s)
        {
            int b = int.Parse(s);
            if (b % 7 == 0)
            {
                Console.WriteLine("这个数与7相关");
            }
           else if (s.Contains("7"))
            {
                Console.WriteLine("这个数与7相关");
            }
            else
            {
                Console.WriteLine("这个数与7无关");
            }
        }
       /// <summary>
       /// 阶乘
       /// </summary>
       /// <param name="j"></param>
       /// <returns></returns>
        public int jiechen(int j)
        { 
            int  sum=1;
        for(int i=1;i<=j;i++)
        {
        sum*=i;
        }
        return sum;
        }
        
        /// <summary>
        /// 一元二次方程
        /// </summary>
        /// <param name="a"></param>
        /// <param name="b"></param>
        /// <param name="c"></param>
        public void ecfc(double a,double b,double c,out double x1,out double x2)
        {
           
           
            x1 = 0;
            x2 = 0;
            if (a == 0)
            {
                Console.WriteLine("这不是一个一元二次方程：");

            }
            else
            {
                double d = b * b - 4 * a * c;
                if (d > 0)
                {
                    x1 = (-b - Math.Sqrt(d)) / (2 * a);
                    x2 = (-b + Math.Sqrt(d)) / (2 * a); 
                    Console.WriteLine("这个方程有两个根:x1={0},x2={1}" , x1, x2);
                }
                else if (d == 0)
                {
                    x1 = x2 = -b / 2 * a;
                       Console.WriteLine("这个方程有一个根x1=x2={0}：",x1);
                }
                else
                {
                    Console.WriteLine("这个方程没有根");
                }
            }
        }
        static void Main(string[] args)
        {
          /*  Console.Write("请输入一个数:");
            int a = int.Parse(Console.ReadLine());
            Program p = new Program();
            p.pdsbszs(a);*/

           /* Console.Write("请输入一个数:");
            string a = Console.ReadLine();
            Program p = new Program();
            p.y7(a);
            Console.ReadLine();*/

          /*  Console.Write("请输入一个数:");
            int a = int.Parse(Console.ReadLine());
            Program j = new Program();
            int n = j.jiechen(a);
            Console.WriteLine(n);
            Console.ReadLine();*/
            while (true)
            {
                Console.Write("请输入a:");
                double r = double.Parse(Console.ReadLine());
                Console.Write("请输入b:");
                double e = double.Parse(Console.ReadLine());
                Console.Write("请输入c:");
                double g = double.Parse(Console.ReadLine());
                double x1;
                double x2;
                Program j = new Program();
                j.ecfc(r, e, g, out x1, out x2);

            }
            Console.ReadLine();
        }
    }
}