Review knowledge point 7: Circular exercises

Table of contents

Exercise 1:

Exercise 2: Find the square root

Exercise 3: Finding Prime Numbers

get random number

Generate random numbers

Exercise 1:

Tips: 

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The first three exercises are used for review and consolidation, and the last one is learning and practicing about random numbers

Exercise 1:

public class LoopTest1 {
    public static void main(String[] args) {
        //分析
        //个位数  十位数  7的倍数
        //123456过 8 9 10 11 12 13 14 15 16 过 ....

        // 1. 得到1~100 之间的每一个数字
        //开始:1
        //结束:100
        for (int i = 1; i <= 100; i++) {
            //2.判断每一个数字,如果符合规则,就打印过, 通过不符合规则就打印真实的数字
            if (i % 10 == 7 || i / 10 % 10 == 7 || i * 10 == 0) {
                System.out.println("过");
                continue;
            }
            System.out.println(i);
        }
    }
}

The result can be run and viewed by itself (because the result is too long)

Exercise 2: Find the square root

analyze:

Analysis 
Square root of 36 Square root 4 
       Square root of 4 

 2 1 * 1 = 1 < 10 
 2 * 2 = 3 < 10 
 3 * 3 = 9 < 10 
 4 * 4 = 16 < 10 5 
 * 5 = 25 < 10 
Inference: The square root of 10 is between 3 and 4

import java.util.Scanner;

public class LoopTest2 {
    public static void main(String[] args) {

        //1. 键盘录入一个整数
        Scanner sc = new Scanner(System.in);
        System.out.println("请录入一个整数");
        int number = sc.nextInt();
        //2. 从1开始循环判断
        //开始 : 1  结束 : number
        for (int i = 1; i <= number; i++) {
            //用 i* i 再用number进行比较
            if (i * i == number){
                System.out.println(i + " 就是" + number + "的平方根的整数部分");
                break;
            }else if (i * i > number){
                System.out.println(i + " 就是" + number + "的平方根的整数部分");
                break;
            }
        }
    }
}

The results can be run and viewed by yourself (don't give yourself an excuse to be lazy)

Exercise 3: Finding Prime Numbers

import java.util.Scanner;

public class LoopTest3 {
    public static void main(String[] args) {


        //1.键盘录入一个整数
        Scanner sc = new Scanner(System.in);
        System.out.println("请录入一个整数");
        int number = sc.nextInt();

        //定义一个变量,表示标记
        //标记着 number 是一个质数
        //true :是一个质数
        //false : 不是一个质数

        //表示最初就认为 number 是一个质数
        boolean flag = true;

        //2. 判断
        //写一个循环, 从2开始判断,一直判断到 number - 1 为止
        //看这个范围之内,有没有数字可以被 number 整除
        for (int i = 2; i < number; i++) {
            // i 依次表示这个范围之内的每一个数字
            //看number是否能被 i 整除就可以了
            if (number % i ==0){
                flag = false;
                break;
            }
        }

        //只有当这个循环结束了,表示这个范围之内所有的数字都判断完毕了
        //此时才能断定number是一个质数
        if (flag){
            System.out.println(number + "是一个质数");
        }else {
            System.out.println(number + "不是一个质数");
        }
    }
}

 The results can be run and viewed by yourself (don't give yourself an excuse to be lazy)

get random number

Java helps us write a class called Random, which can generate a random number

Generate random numbers

Judgment skills:

In the parentheses, the writing accepts the range of generating random numbers

This range must start from 0 and end with this number - 1

Motto: wrap the head but not the tail, wrap the left but not the right

Exercise 1:

 

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

public class LoopTest10 {
    public static void main(String[] args) {
        //随机数范围 1-100
        Random r = new Random();
        int number = r.nextInt(100)+1;//0~100+1
        //2. 猜数字是多少
        Scanner sc =new Scanner(System.in);
        while (true){
            System.out.println("请输入你的数字");
            int guessnumber = sc.nextInt();
            if (guessnumber > number){
                System.out.println("大了");
            }else if(guessnumber < number ){
                System.out.println("小了");
            }else{
                System.out.println("恭喜你,猜中了");
                break;
            }
        }
    }
}

result:

Tips: