c#之课后习题

1.折叠代码

#region

折叠内容
#endregion

2.保留三位小数

using System;

namespace _005_double保留3位小数
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("输入三位数，依次按Enter结束：");
            double a = double.Parse(Console.ReadLine());
            double b = double.Parse(Console.ReadLine());
            double c = double.Parse(Console.ReadLine());
            Console.WriteLine("{0:f3}",a);
            Console.WriteLine("{0,10:f3}",b);
            Console.WriteLine("{0,10:f3}",c);
        }

    }
}

3.求水仙花数

using System;

namespace _001_水仙花数
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] numbers = new int[3];
            int sum = 0;
            for (int num = 100; num < 1000; num++)
            {
                numbers[0] = num / 100 ;
                numbers[1] = num %100/10;
                numbers[2] = num  % 100%10;
                //for (int i = 0; i < 3; i++)
                //{
                //    sum += (int)Math.Pow(numbers[i], 3);
                //}
                sum = numbers[0] * numbers[0] * numbers[0] + numbers[1] * numbers[1] * numbers[1] + numbers[2] * numbers[2] * numbers[2];
                if (num == sum)
                {
                    Console.WriteLine("水仙花数为：" + num);
                }
            
            }
        }
    }
}

 4.

四舍五入并保留两位小数
double d =3.1415926;
d= Math.Round(d,2);
Console.WriteLine("{0,10:f2}",d)//另一种方法，冒号前位10的倍数，显示小数点前有多少字节,f后要保留的小数 位数

using System;

namespace _008_四舍五入
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("输入以为正数：");
            double a = Double.Parse(Console.ReadLine());
            int result = (int)(a + 0.5);

            //double b = Math.Ceiling(a);//向上进位取整
            ////double b = Math.Floor(a);//向下进位取整
            Console.WriteLine(result);
        }
    }
}

5.

编一个程序，用while循环语句来计算1+1/2+2/3+3/4+...+99/100之和。

using System;

namespace _013_while求和
{
    class Program
    {
        static void Main(string[] args)
        {
            double i = 1;
            double sum = 1;
            while (i<=100)
            {
                sum =sum+(i-1)/i ;
                i++;
            }
            Console.WriteLine("和为{0}",sum);
        }
    }
}

6.

编写一个程序，用for语句，求出1+(1+2)+(1+2+3)+...+(1+2+3+...+10)之和。

using System;

namespace _014_for求和
{
    class Program
    {
        static void Main(string[] args)
        {
            int sum = 0;
            int sum1 = 0;
            for (int i = 1; i <=10; i++)
            {
                     sum = sum + i;
                    sum1 = sum1 + sum;
            }
            Console.WriteLine(sum1);
        }
    }
}

7.编一个程序，要求使用while语句，输入用户名和密码，实现用户登录程序的功能，至多允许输入三次，超过三次不允许登录。

using System;

namespace _016_加分题2
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("请输入用户名和密码：");
            int count = 0;
            while (count <3)
            {
                string name = Console.ReadLine();
                string password = Console.ReadLine();
                if (name == "huang" && password == "154090")
                {
                    Console.WriteLine("登录成功");
                    break;
                }
                else
                    Console.WriteLine("错误，请重新输入！");
                count++;
            }

        }
    }
}

8.求出1~1000之间的所有能被7整除的数，并计算和输出每5个的和。

using System;

namespace _005_能被7整除的数
{
    class Program
    {
        static void Main(string[] args)
        {
            int count = 0;
            int sum = 0;
            for(int i = 1; i <= 1000; i++)
            {
                if ( i % 7 == 0)
                {
                    sum += i;
                    count++;
                    Console.WriteLine(i);
                }
                if(count == 5)
                {
                    Console.WriteLine(sum);
                    sum = 0;
                    count = 0;
                }
            }
           
        }
    }
}

8.,编写一个控制台程序，分别输出1~100之间的平方、平方根。 

using System;

namespace _006_1_100之间的平方平方根
{
    class Program
    {
        static void Main(string[] args)
        {
            
            for (int i= 1; i <= 100; i++)
            {
                double a = Math.Pow(i, 0.5);//平方
                double b = Math.Pow(i, 2);
              //double gen = Math.Sqrt(i);//这个方法可以取得一个数字的平方根
            Console.WriteLine("{2}的平方为{0}，平方根为{1}",b,a,i);
                
            }
            
        }
    }
}

9.判断月份天数

using System;

namespace _009_输出该月天数
{
    class Program
    {
        static void Main(string[] args)
        {
            //闰年：2月29     1，3，5，7，---31天    4，6，9,11---30     8，10，12----31
            //平年：28        
            Console.WriteLine("请输入年份，月份，分别按Enter结束");
            int year = int.Parse(Console.ReadLine());
            int month = int.Parse(Console.ReadLine());
             
            if (year % 400 == 0 || year % 4 == 0 && year % 100 != 0)//闰年情况下
            {
                 if(month % 2 != 0&&month<8)
                    {
                        Console.WriteLine("31天");
                    }
                    else if(month == 2)
                    {
                        Console.WriteLine("29天");
                    }
                    else if(month % 2 == 0 && month < 8)
                    {
                        Console.WriteLine("30天");
                    }
                    else if (month % 2 == 0 && month >= 8)
                    {
                        Console.WriteLine("31天");
                    }
                    else if (month% 2 != 0 && month >= 8)
                    {
                        Console.WriteLine("30天");
                    }
                }
            else
            {
                if (month % 2 != 0 && month < 8)
                {
                    Console.WriteLine("31天");
                }
                else if (month == 2)
                {
                    Console.WriteLine("28天");
                }
                else if (month % 2 == 0 && month < 8)
                {
                    Console.WriteLine("30天");
                }
                else if (month % 2 == 0 && month >= 8)
                {
                    Console.WriteLine("31天");
                }
                else if (month % 2 != 0 && month >= 8)
                {
                    Console.WriteLine("30天");
                }
            }
            }

        }
    }

10.1-1000之间的素数

using System;

namespace _020_1_1000之间的素数
{
    class Program
    {
        static void Main(string[] args)
        {
            for (int i = 2; i < 1001; i++)
            {
                bool sushu = true;//布尔类型
                for (int j = 2; j <=i-1; j++)
                {
                    if (i % j == 0)
                    {
                        sushu = false;
                        break;
                    }
                }
                if (sushu)
                {
                    Console.WriteLine(i);
                }
            }
            
        }
    }
}

11.九九乘法表

using System;

namespace _021__九九乘法表
{
    class Program
    {
        static void Main(string[] args)
        {
            //第一种格式
            //for (int i = 1; i < 10; i++)
            //{
            //    for (int j = 1; j < 10; j++)
            //    {
            //        Console.Write(i+"*"+j+"="+(i*j)+"	");//不换行
            //    }
            //    Console.WriteLine();//什么都没有表示换行
            //}


            //第二种格式
            for (int i = 1; i < 10; i++)
            {
                for (int j = 1; j <= i; j++)
                {
                    Console.Write(i + "*" + j + "=" + (i * j) + "	");//不换行
                }
               Console.WriteLine();//什么都没有表示换行
            }
        }
    }
}

12.

生成随机数
Random random = new Random();//创建一个可以生成随机数的对象
int num = random.Next(1,7);//给一个范围，取不到最大值
Console.WriteLine(num);

using System;

namespace _022_掷骰子_打印各种点数的出现次数
{
    class Program
    {
        static void Main(string[] args)
        {
            int num1 = 0, num2 = 0, num3 = 0, num4 = 0, num5 = 0, num6 = 0;
            Random random = new Random();//创建随机数
            for (int i = 0; i < 100; i++)
            {
                
                int num = random.Next(1, 7);//范围1到6
                switch (num)
                {
                    case 1:
                        num1++;
                        break;
                    case 2:
                        num2++;
                        break;
                    case 3:
                        num3++;
                        break;
                    case 4:
                        num4++;
                        break;
                    case 5:
                        num5++;
                        break;
                    case 6:
                        num6++;
                        break;
                }
            }
            Console.WriteLine(num1);
            Console.WriteLine(num2);
            Console.WriteLine(num3);
            Console.WriteLine(num4);
            Console.WriteLine(num5);
            Console.WriteLine(num6);
        }
    }
}

13.金字塔

using System;

namespace _004_金字塔
{
    class Program
    {
        static void Main(string[] args)
        {
            for (int i = 0; i < 9; i++)
            {
                for (int j = i; j < 8; j++)
                {
                    Console.Write(" ");
                }
                for (int z = 0; z <= 2*i; z = z + 1)
                {
                    Console.Write("*");
                }
                Console.WriteLine();
            }
           
        }

    }
    }

14.四舍五入

using System;

namespace _006_四舍五入
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("输入一位正数：");
            double a = Double.Parse(Console.ReadLine());
            //int result = (int)(a + 0.5);这方法也可以
            a = Math.Round(a, 0);
            //double b = Math.Ceiling(a);//向上进位取整
            ////double b = Math.Floor(a);//向下进位取整
            Console.WriteLine(a);


        }
    }
}

15.枚举之星期

using System;

namespace _010_QQ状态
{
    public enum QQ
    {
        OnLine=1,
        OffLine=2,
        Leave=3,
        Qme=4,
        Busy=5
    }
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("输入数字");

            int index = int.Parse(Console.ReadLine());
            QQ num = (QQ)index;
            switch (num)
            {
                case QQ.OnLine:
                case QQ.OffLine:
                case QQ.Leave:
                case QQ.Qme:
                case QQ.Busy:
                   
                    Console.WriteLine(num);
                    break;
                default:
                    Console.WriteLine("超出范围");
                    break;


            }
        }
    }
}

16。键盘输入红包金额，包数

1.
using System;





namespace _001_随机红包System.Security.Cryptography.RNGCryptoServiceProvider
{

    class Program
    {
        static void Main(string[] args)
        {

            //微信红包
            Console.WriteLine("请输入红包金额和数量:");
            int money = int.Parse(Console.ReadLine());
            int num = int.Parse(Console.ReadLine());
            int dollar = money * 100;
            int temp = 0;
            Random a = new Random();
            for (int i = 0; i < num - 1; i++)
            {
                int b = a.Next(1, dollar - temp);
                if (b > dollar / 2)
                {
                    i--;
                    continue;
                }
                temp += b;

                if (temp == dollar)
                {
                    temp = 0;
                    i = 0;
                    continue;
                }
                Console.WriteLine(b / 100.0);
            }
            Console.WriteLine((dollar - temp) / 100.0);
        }
    }
}


2.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            while (true)
            {
                Console.WriteLine("请输入金额（例如：100.00）");
                double money = Math.Round(Convert.ToDouble(Console.ReadLine()), 2);
                Console.WriteLine("请输入红包个数");
                int count = Convert.ToInt32(Console.ReadLine());
                List<double> listMoney = new List<double>();
                for (int i = 0; i < count; i++)
                {
                    Random random = new Random();
                    if (i == 0)
                    {
                        listMoney.Add(money);
                        continue;
                    }
                    double maxMoney = listMoney.Max();
                    int maxIndex = listMoney.IndexOf(maxMoney);
                    double rd = random.NextDouble();
                    double m = Math.Round(maxMoney * rd, 2);
                    listMoney[maxIndex] = maxMoney - m;
                    listMoney.Add(m);
                }
                Console.WriteLine("分别获得红包");
                foreach (var item in listMoney)
                {
                    Console.WriteLine("{0}	元", item.ToString("N"));
                }
                //测试，计算金额是否正确
                Console.WriteLine("合计：{0}元

", listMoney.Sum().ToString("N"));
                Console.WriteLine("按任意键继续

");
                Console.ReadKey();
            }

        }
    }
}