递归讲解

package method;

import java.util.Scanner;

public class Demo07 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System .in);
        System.out.println("请输入计算的第一个数||输入非数字退出！！！");
        while (scanner.hasNextDouble()){
            String next = scanner.next();
            double a = scanner.nextDouble();
            System.out.println("请输入运算符：【+、-、*、/】");
            String c = scanner.next();
            System.out.println("请输入计算的第二个数");
            double b = scanner.nextDouble();
            switch (c){
                case "+":
                    double add = add(a, b);//因为a和b的值是用户在键盘上输入
                                           //不需要有值 a，b就可以
                    System.out.println(add);
                    break;
                case "-":
                    double subtract = subtract(a, b);
                    System.out.println();
                    break;
                case "*":
                    double multiply = multiply(a, b);
                    System.out.println(multiply);
                    break;
                case "/":
                    double divide = divide(a, b);
                    System.out.println(divide);
                    break;
                    default:
                        System.out.println("运算符输入错误！");
                        break;
            }
            System.out.println("请继续输入计算的第一个数||输入非数字退出！！！");
        }
        scanner.close();

    }
    public static double add(double n1,double n2){
        return n1+n2;
    }
    public static double subtract(double n1,double n2){
        return n1-n2;
    }
    public static double multiply(double n1,double n2){
        return n1*n2;
    }
    public static double divide(double n1,double n2){
        return n1/n2;
    }
}