2024/9/27

登录系统（验证码）：
import java.util.ArrayList;
import java.util.Random;
import java.util.Scanner;

public class Registration {
public static void main(String[] args) {
ArrayList list = new ArrayList();
Scanner sc = new Scanner(System.in);
int choice;
while (true) {
System.out.println("1.注册");
System.out.println("2.登录:");
choice = sc.nextInt();
switch (choice) {
case 1:
zhuce(list);
break;
case 2:
denglu(list);
break;
}
}

}

public static void zhuce(ArrayList<User> list) {

    String username, password;
    User user = new User();
    Scanner sc = new Scanner(System.in);
    System.out.println("请输入您的用户名:");
    username = sc.nextLine();
    user.setUsername(username);
    System.out.println("请输入您的密码:");
    password = sc.nextLine();
    user.setPassword(password);
    list.add(new User(username, password));
}

public static void denglu(ArrayList<User> list) {

    User user = list.get(0);
    String username, password;
    Scanner sc = new Scanner(System.in);
    while (true) {
    System.out.println("用户名:");
    username = sc.nextLine();
    System.out.println("密码:");
    password = sc.nextLine();
        if (username.equals(user.getUsername()) && password.equals(user.getPassword())) {
            Random r = new Random();
            String code = "";
            for (int i = 1; i <= 6; i++) {
                int type = r.nextInt(3);
                switch (type) {
                    case 0:
                        code += r.nextInt(10);
                        break;
                    case 1:
                        char ch1 = (char) ('a' + r.nextInt(26));
                        code += ch1;
                        break;
                    case 2:
                        char ch2 = (char) ('A' + r.nextInt(26));
                        code += ch2;
                        break;
                }
            }
            System.out.println("密码正确，请等待验证码并输入");
            System.out.println("验证码为:" + code);
            System.out.println("请输入验证码：");
            String yanzheng = sc.nextLine();
            if (yanzheng.equals(code)) {
                System.out.println("登录成功！");
                break;
            }
        } else System.out.println("用户名或密码错误，请重新输入:");
    }

}

}

public class User {
String username;
String password;

public User() {
}

public User(String username, String password) {
    this.username = username;
    this.password = password;
}

public  String getUsername() {
    return username;
}

public void setUsername(String username) {
    this.username = username;
}

public String getPassword() {
    return password;
}

public void setPassword(String password) {
    this.password = password;
}

}

四则运算：

include

include

include

include

include

using namespace std;

int main(){

for(int i=0;i<30;i++){
int a=rand()%100;
int b=rand()%100;
int c=rand()%4;
    switch(c){
case 0:
    cout<<a<<"+"<<b<<"="<<endl;
    break;
case 1:
    cout<<a<<"-"<<b<<"="<<endl;
    break;
case 2:
    cout<<a<<"*"<<b<<"="<<endl;
    break;
case 3:
    cout<<a<<"/"<<b<<"="<<endl;
    break;


}
}




return 0;

}