4.28

package zuoye11;

import java.util.Random;
import java.util.Scanner;

public class Menu {

    public static void main(String[] args) {
        mainMenu();
    }
    
         public static void mainMenu() {
             Scanner input = new Scanner(System.in);
             System.out.println("****************Menu**************");
             System.out.println("\t\t1.注册");
             System.out.println("\t\t2.登录");
             System.out.println("\t\t3.幸运抽奖");
             System.out.println("\t\t4.看小故事");
             System.out.println("\t\t5.退出系统");
             System.out.println("*****************************************");
             System.out.println("\n请选择菜单:");
             int i = input.nextInt();
             switch (i) {
                case 1:
                    login();break;
                case 2:
                    zhuce();break;
                case 3:
                    choujiang();break;
                case 4:
                    xiaogushi();break;
                case 5:
                    System.out.println("退出系统");
                default:
                    System.out.println("输入错误！");
                    returnMain();
                    break;
                }
            }
             
        private static void zhuce() {
                Scanner input=new Scanner(System.in);
                System.out.println("请输入用户名：");
                String name=input.next();
                System.out.println("请输入密码：");
                String password=input.next();             
                if(name.equals("李四")&&password.equals("123456")) {
                    System.out.println("注册成功");
                }else {
                    System.out.println("注册失败");
                }
                returnMain();
            }
         
         private static void login() {
            Scanner input=new Scanner(System.in);
            System.out.println("请输入用户名：");
            String name=input.next();
            System.out.println("请输入密码：");
            String pwd=input.next();
            if(name.equals("李四")&&pwd.equals("123456")) {
                System.out.println("登录成功");
            }else {
                System.out.println("登录失败");
            
            }
            returnMain();
        }
         private static void choujiang() {
                Scanner input=new Scanner(System.in);
                Random r=new Random();
                System.out.println("请输入一个四位数：");
                int x=input.nextInt();
                int y=r.nextInt(10);
                if(x/100%10==y) {
                    System.out.println("幸运会员");
                }else {
                    System.out.println("很遗憾您不是幸运会员");
                }
                returnMain();
                
            }
          private static void xiaogushi() {
                Scanner input=new Scanner(System.in);
                System.out.println("请选择您要看的小故事：1.格林童话");
                int z=input.nextInt();
                switch(z) {
                case 1:
                    System.out.println("格林童话");
                default:
                    System.out.println("没有该图书！");
                }
                returnMain();
            }
          public static void returnMain(){
                System.out.println("是否返回主菜单?Y/N");
                Scanner input = new Scanner(System.in);
                if (input.next().equalsIgnoreCase("Y")) {
                    mainMenu();
                }else{
                    System.out.println("谢谢使用");
                }
           }
}

package zuoye11;

import java.util.Scanner;

public class zuoye11 {

    public static void main(String[] args) {
        int sum=1;
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个整数：");
        int k = sc.nextInt();
        for (int i = 1; i <= k; i++) {
            sum=sum*i;
        }
        System.out.println(k+"的阶乘为："+sum);
    }
}

package zuoye11;

public class zuoye11 {
    public static void main(String[] args) {
        near(2020);
    }
        public static void near(int y){
             if (y % 4 == 0 && y % 100 != 0 || y % 400 == 0) {
                    System.out.println(y + "年是闰年");
                } else {
                    System.out.println(y + "年不是闰年");
                }
        }

}