计算器的代码实现 还是不知道怎么进行累加

import java.util.Scanner;

public class Test4 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入一个数字：");
        while (scanner.hasNextDouble()) {
            double e = scanner.nextDouble();
            System.out.println("请再输入一个数字：");
            double f = scanner.nextDouble();
            System.out.println("请选择算法 加 减 乘 除：");
            String k = scanner.next();
            switch ( k) {
                case "+":
                    System.out.println((e + f));
                    break;
                case "-":
                    System.out.println((e - f));
                    break;
                case "*":
                    System.out.println((e * f));
                    break;
                case "/":
                    System.out.println((e / f));
                    break;
                default:
                    System.out.println("请输入正确的算法符号");


            }
        }
        scanner.close();
    }
}