poorly written calculator thingy

import java.util.Scanner;

public class Calculator {
    public static void main(String args[]) {
        double a, b;
        double answer=0;
        boolean cont;
        String operation;
        Scanner scanner = new Scanner(System.in);
        System.out.println("First Number: ");
        a = scanner.nextDouble();
        System.out.println("Operation: ");
        operation = scanner.next();
        System.out.println("Second Number: ");
        b = scanner.nextDouble();

        switch (operation) {
            case "+":
                answer = a + b;
                break;
            case "-":
                answer = a - b;
                break;
            case "*":
                answer = a * b;
                break;
            case "/":
                answer = a / b;
                break;
            default:
                System.out.println("Operation cannot be performed");
        }
        System.out.println("Your answer is = " + answer + "\nContinue?");

        if (scanner.next().equalsIgnoreCase("yes")) {
            cont = true;
            while (cont) {
                System.out.println("Operation: ");
                operation = scanner.next();
                System.out.println("Number: ");
                b = scanner.nextDouble();
                switch (operation) {
                    case "+":
                        answer = answer + b;
                        break;
                    case "-":
                        answer = answer - b;
                        break;
                    case "*":
                        answer = answer * b;
                        break;
                    case "/":
                        answer = answer / b;
                        break;
                    default:
                        System.out.println("Operation cannot be performed");
                }
                System.out.println("Your answer is = " + answer + "\nContinue?");
                if (scanner.next().equalsIgnoreCase("yes")) {
                    cont = true;
                } else {
                    cont = false;
                }
            }
        }
    }
}