"Hundred Days, One Hundred Questions · Basics" Prepare for the interview, insist on brushing up the fifth chapter - loop statement (2)!

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JAVA13 average number [loop statement]

topic:

answer:

import java.util.Scanner;

public class Main {
    
    
    public static void main(String[] args) {
    
    
        Scanner scan = new Scanner(System.in);
        int num;
        int sum = 0,count = 0;
        while(true){
    
    
            num=scan.nextInt();
            if(num<0)break;
            count++;
            sum+=num;
        }
        //没有下面这行代码的一律不及格
        scan.close();
        if(count>0){
    
    
            double avg=(double)sum/count;
            System.out.println(String.format("%.2f",avg));
        }
    }
}

JAVA14 judge prime number [loop statement]

topic:

answer:

import java.util.Scanner;

public class Main {
    
    
    public static void main(String[] args) {
    
    
        Main main = new Main();
        Scanner scan = new Scanner(System.in);
        int number = scan.nextInt();
        System.out.println(main.isPrimeNumber(number));
    }

    public Boolean isPrimeNumber(int number) {
    
    
        if (number == 2) return true;//判断质数从2开始
        int i = 3 ; //若不是2 , 依次判断3,5,7,9···
        if (number != 2 && number % 2 == 0) return false;//质数是不等于2的奇数
        for (; number % i != 0; i += 2); //当能整除某个奇数时退出循环
        return i == number ? true :false; //判断是否是因为整除自己才退出循环
    }
}

JAVA15 calculates the number of integer digits [operator]

topic:

answer:

import java.util.Scanner;
public class Main {
    
    
    public static void main(String[] args) {
    
    
        Scanner scanner = new Scanner(System.in);
        double d= scanner.nextDouble();
        scanner.close();
        //好家伙，这也太强了，简单粗暴
        int i = (int)(d+0.5);
        System.out.println(i);
    }
}