四则运算

package 软件工程;


import java.util.Scanner;

public class szys {
    public static void main(String[] args) {
boolean a=true;
        while (a==true) {
            Scanner scanner = new Scanner(System.in);
            System.out.println("请输入第一个数字");
            double num1 = scanner.nextDouble();
            System.out.println("请输入运算符");
            String ysf = scanner.next();
            System.out.println("请输入另一个数字");
            double num2 = scanner.nextDouble();
            switch (ysf) {
                case "+":
                    System.out.println(num1 + num2);
                    break;
                case "-":
                    System.out.println(num1 - num2);
                    break;
                case "*":
                    System.out.println(num1 * num2);
                    break;
                case "/":
                    if (num2 == 0) {
                        System.out.println("分母为零运算不成立");
                       break;
                    } else
                        System.out.println(num1 / num2);
                    break;
                default:
                    System.out.println("请输入正确的运算符");
            }
            System.out.println("输入q即可退出程序，输入其他即可继续程序");
            String b=scanner.next();
            if (b=="q"){
                a=false;
            }else {
                break;
            }




        }

    }
}