int n1 = Convert.ToInt32(Console.ReadLine());
int n2 = Convert.ToInt32(Console.ReadLine());
while (n2 >= n1)
{
    if (n2 % 2 == 0) { Console.WriteLine(n2); }
    n2--;
}
while (n2 <= n1)
{
    if (n1 % 2 == 0) { Console.WriteLine(n1); }
    n1--;
}

 int n = Convert.ToInt32(Console.ReadLine());
 int a=n;
 while (n>0)
 {
     a += --n; 
 }
 Console.WriteLine(a);

视频前，自己想出来一个，也一样。

自己尝试了一下n1到n2之间的所有偶数：

int n1 = Convert.ToInt32(Console.ReadLine());
int n2 = Convert.ToInt32(Console.ReadLine());
while (n1 < n2+1) {
    if (n1 % 2 == 0) { Console.WriteLine(n1); }
    n1++;
}

using System;

namespace _018_循环语句_while循环
{
    class Program
    {
        static void Main(string[] args)
        {
            //int n = Convert.ToInt32(Console.ReadLine());
            //int i = 1;
            //int sum = 0;
            //while (i < n + 1)
            //{
            //    sum += i;
            //    i++;
            //}
            //Console.WriteLine(sum);


            //int i = 1;
            //while (i < 101)
            //{
            //    // 1-100
            //    if (i % 2 == 0)
            //    {
            //        Console.WriteLine(i);
            //    }
            //    i++;
            //}


            // 10 15
            //int i = 10;
            //while (i < 16)
            //{
            //    Console.WriteLine(i);
            //    i++;
            //}

            int n1 = Convert.ToInt32(Console.ReadLine());
            int n2 = Convert.ToInt32(Console.ReadLine());

            int i = n1;
            while (i < n2 + 1)
            {
                if (i % 2 == 0)
                {
                    Console.WriteLine(i);
                }
                i++;
            }

        }
    }
}

和老师 不一样的方法

        //❓输⼊两个整数n1,n2,输出n1 - n2(包含n1和n2)之间所有的偶数。

            int n1 = Convert.ToInt32(Console.ReadLine());
            int n2 = Convert.ToInt32(Console.ReadLine());
            if (n1 > n2)
            {
                int n3 = n1;
                n1 = n2;
                n2 = n3;
            }
            int a = n1;
            if (a % 2 == 0)
            {
                Console.WriteLine(a);
                while (a >= n1 && a <= n2 - 2)
                {
                    a += 2;
                    Console.WriteLine(a);
                }
            }
            if (a % 2 != 0)
            {
                a += 1;
                Console.WriteLine(a);
                while (a >= n1 && a <= n2 - 2)
                {
                    a += 2;
                    Console.WriteLine(a);
                }
            }

int.parse

        static void test11()
        {
            Console.WriteLine("请输入整数n1：");
            int n1 = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("请输入整数n2：");
            int n2 = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("你输入的n1是：{0},你输入的n2是：{1}",n1,n2);
            int i = n1;
            if (n2>n1)
            {
                while (i<=n2)
                {
                    if (i%2==0)
                    {
                        Console.WriteLine(i);
                    }                   
                    i++;
                }
            }
            else
            {
                while (i >= n2 )
                {
                    if (i % 2 == 0)
                    {
                        Console.WriteLine(i);
                    }
                    i--;
                }
            }         
        }

12345678900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

int i=1;

while (i<101）

{

      if( i%2==0){

            Console.WriteLine(i);

       }

      i++;

}

int n1;   

int n2;

while (n1<n2)

{

     if(n1%2==0){

         Console.WriteLine(n1)

      }

     n1+1;

}

可以在while语句中插入if语句

第五十二课  控制while循环的开头和结尾

1. 输入两个整数n1,n2，输出n1-n2（包含n1和n2）之间所有的偶数。

int n1 = Convert.ToInt32(Console.ReadLine());
int n2 = Convert.ToInt32(Console.ReadLine());
            if (n1 > n2)
            {
                int temp = n1;
                n1 = n2;
                n2 = temp;
                Console.WriteLine("{0}、{1}", n1, n2);
            }

            while (n1 < n2 + 1)
            {
             if (n1 % 2 == 0)                
             Console.Write(n1+" ");                
             n1++;            
            }

学这玩应掉头发！

2. 3n+1问题：

对于任意大于1的自然数n，若n为奇数，将n变成3n+1，否则变成n的一半，经过若干次这样的变化，n最终一定会变成1,。比如：7→22→11→34→17→52→26→13→40→20→10→5→16→8→4→2→1

输入n，输出变换的次数。

比如输入3，输出7；输入10，输出6。

int n =Convert.ToInt32(Console.ReadLine());
            int a = 0;
            while (n > 1)
            {
                if(n % 2 == 1)
                {
                    n = 3 * n + 1;
                    a++;
                }
                else
                {
                    n = n / 2;
                    a++;
                }                
            }
            Console.Write("最后值为{0}" + " " + "共用{1}步", n, a);

这道题还蛮好玩的，睡觉去了，睡晚了更掉头发，明天再听老师揭秘。

%是求余的意思

/是相除的意思