第三天、运算符

一、java运算符

1.1算术运算符

1.2赋值运算符

1.3关系运算符

1.4逻辑运算符

1.5位运算符

1.6位移运算符

1.7三元运算符

1. 条件表达式？成立表达式：未成立表达式
2. 实例：3>2 ? “是的”：“不是的”

二、进制

2.1常用进制

2.2十进制转任意进制

• 使用短除法，除以该进制直到商为零 ，结果就是从最后一个余数读到第一个

2.3任意进制转成十进制

• 使用乘权求和，即为：数字*进制^{(位数-1)+……+数字乘进制}0

三、选择结构

3.1单分支if

package com.la;
import java.util.Scanner;
public class If {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入你的成绩");
        int score = scanner.nextInt();
        if(score>=60){
            System.out.println("及格");
        }
        if (score<60){
            System.out.println("不及格");
        }
    }
}

3.2if…else

import java.util.Scanner;
public class If {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入你的成绩");
        int score = scanner.nextInt();
        if(score>=60){
            System.out.println("及格");
        }
        if (score<60){
            System.out.println("不及格");
        }
        ifElse();
    }
    public static void ifElse(){
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入你的成绩");
        int score = scanner.nextInt();
        if(score>=60){
            System.out.println("及格");
        }else {
            System.out.println("不及格");
        }
    }
}

3.3多分支if

package com.la;
import java.util.Scanner;
public class ElseIf {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入你的成绩");
        int score = scanner.nextInt();
        if (score>=80){
            System.out.println("优秀");
        }else if (score>=60&&score<80){
            System.out.println("及格");
        }else {
            System.out.println("未及格");
        }

    }
}

3.4嵌套if

package com.la;
import java.util.Scanner;
public class NestIf {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入你的成绩");
        int score = scanner.nextInt();
        if (score>60){
            System.out.println("已及格");
            if (score>=80){
                System.out.println("优秀");
            }else {
                System.out.println("良好");
            }
        }else {
            System.out.println("未及格");
        }
    }
}

四、练习

4.1统计年龄层次比例

package com.la;
import java.math.BigDecimal;
import java.util.Scanner;
public class work1 {
    static int count;
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        for (int i = 1; i < 11; i++) {
            System.out.print("请输入第"+i+"的年龄：");
            int age = scanner.nextInt();
            if (age<30){
                count++;
            }
        }
        BigDecimal a = new BigDecimal(count);
        BigDecimal b = new BigDecimal(10);
        BigDecimal f = new BigDecimal(100);
        BigDecimal d = new BigDecimal(1);
        BigDecimal c = a.divide(b);
        System.out.println(count);
        System.out.println((double) (count/10));
        System.out.println("30岁以下的比例："+c.multiply(f)+"%");
        System.out.println("30岁以上的比例："+(d.subtract(c)).multiply(f)+"%");
    }
}

4.2求商品折扣

package com.la;
import java.util.Scanner;
public class work2 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入商品总价格");
        int totalPrice = scanner.nextInt();
        double discount;
        if (totalPrice==550){
            discount=1;
            System.out.println("折扣后总价为："+totalPrice*discount);
        }else if (totalPrice>=500){
            discount=0.5;
            System.out.println("折扣后总价为："+totalPrice*discount);
        }else if (totalPrice>=400&&totalPrice<500){
            discount=0.6;
            System.out.println("折扣后总价为："+totalPrice*discount);
        }else if (totalPrice>=300&&totalPrice<400){
            discount=0.7;
            System.out.println("折扣后总价为："+totalPrice*discount);
        }else if (totalPrice>=200&&totalPrice<300){
            discount=0.8;
            System.out.println("折扣后总价为："+totalPrice*discount);
        }else {
            discount=0.9;
            System.out.println("折扣后总价为："+totalPrice*discount);
        }
    }
}

4.3判断奇偶数

package com.la;
import java.util.Scanner;
public class Wrok1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入一个正整数(退出请输0)");
        while (true){
            Integer i = scanner.nextInt();
            if (i%2==0&&i!=0&&i>0){
                System.out.println("该数"+i+"为偶数");
            }else if(i==0) {
                break;
            }else {
                System.out.println("该数"+i+"为奇数");
            }
        }
        }
}

4.4模拟中奖

package com.la;
import java.util.Scanner;
public class Work2 {
    public static void main(String[] args) {
        int v = (int) (Math.random()*10000+1);
        Scanner scanne = new Scanner(System.in);
        System.out.println("请输入你的中奖号码");
        while (true){
            int a=scanne.nextInt();
            if (a==v){
                System.out.println("恭喜你中奖了");
            }else{
                System.out.println("再接再厉！");
            }
            System.out.println("奖励号码公布"+v);
        }
    }
}