编写简单的计算器

思路

1.先写四个方法对应加减乘除
2.用scanner来收集用户数据
3.用switch进行匹配
4.输出结果

import java.util.Scanner;
public class Demo11 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入第一个数：");
        double a = scanner.nextDouble();
        System.out.println("请输入符号：");
        String s = scanner.next();
        System.out.println("请输入第二个数：");
        double b = scanner.nextDouble();

        switch (s){
            case "+":
                System.out.println(add(a,b));
                break;
            case "-":
                System.out.println(subtract(a,b));
                break;
            case "*":
                System.out.println(multiply(a,b));
                break;
            case "/":
                System.out.println(divide(a,b));
                break;

        }
        scanner.close();
    }
    public static double add(double a, double b) {
        return a + b;
    }
    public static double subtract(double a, double b) {
        return a - b;
    }
    public static double multiply(double a, double b) {
        return a * b;
    }
    public static double divide(double a, double b) {
        if (b == 0) {
            System.out.println("算数不合法");
        }
        return a / b;
    }
}

问题

1.在输出nextdouble，nextline，nextdouble时，nextline的数值会被直接跳过

而使用next则正常运行

具体原因参考
2.在设计程序时要考虑程序合法性
在做除法时，应当注意：除以0应该时不合法的。

参考

参考他人代码

package test;
import java.util.Scanner;
public class Calculator {
        public static void main(String[] args) {
            while (true){
                System.out.println("输入用空格隔开，如：（6 + 9）：");
                Scanner sc = new Scanner(System.in);
                double a = sc.nextDouble();

                String s = sc.next();

                double b = sc.nextDouble();

                double result = 0;
                switch (s){
                    case "+":
                        result = add(a,b);
                        break;
                    case "-":
                        result = subtract(a,b);
                        break;
                    case "*":
                        result = multiply(a,b);
                        break;
                    case "/":
                        result = divide(a,b);
                        break;
                    default:
                        System.out.println("输入错误");
                        break;

                }
                System.out.println("输出的结果是："+a+s+b+"="+result);
            }
        }

        public static double add(double x,double y){
            return  x+y ;

        }
        public static double subtract(double x,double y){
            return x-y;
        }
        public static double multiply(double x,double y){
            return x*y;
        }
        public static double divide(double x,double y){
            if (y==0)
                System.out.println("除数不能为0！");

            return x/y;
        }
    }