Java如何使用指定的表达式计算变量的值？

Question

我正在学习Lubomir Stanchev的" 通过游戏学习Java ",这个问题我无法解决.

我们将随机要求玩家添加,乘以或减去一位数字(我们跳过除法,因为除以两个数字的结果不是整数).游戏应该询问10个数学问题并记录答案.最后,游戏应该告诉玩家他们做得多好,也就是他们正确回答了多少问题.

这就是我所拥有的:

import java.util.Scanner;

public class Arithmetic {
    public static void main(String args[]){
        Scanner keyboard = new Scanner(System.in);
        int i, x, y, z, answer, a, counter = 0;
        char sign;
        for(i = 0; i < 10; i++) {
            x = (int)(Math.random() * 10);
            y = (int)(Math.random() * 10);
            a = (int)(Math.random() * 3);//random sign

            if(a==0){
                sign = '+';
            } else if(a == 1) {
                sign = '-';
            } else {
                sign = '*';
            }

            System.out.print(x + " " + sign + " " + y + " = ");
            z = keyboard.nextInt();          
            answer = x + sign + y; 

            System.out.println(answer);

            if(z == answer){
                System.out.println("Correct");
                counter++;                
            } else {
                System.out.println("Wrong");       
            }
        }
        System.out.println("You answered "+counter+" questions correctly");
    }
}

变量答案的值存在问题.它不会计算表达式,因为x和y是整数,而变量符号是char.我来自JS所以我发现这很奇怪.在JS中,无论类型如何,表达式都会自动计算或连接.我在第3章,所以我没有学过parseInt东西,我认为它不适用于char.

谢谢您的帮助.

这是我最新的答案:

public class Arithmetic {
    public static void main(String args[]){
        Scanner keyboard = new Scanner(System.in);
        int i, x, y, z, answer, a, counter=0;
        char sign;
        for(i=0;i<10;i++){
            x = (int)(Math.random() * 10);
            y = (int)(Math.random() * 10);
            a = (int)(Math.random() * 3);//random sign

            if(a==0){
                sign = '+';
                answer = x + y;
            } else if(a==1) {
                sign = '-';
                answer = x - y;
            } else {
                sign = '*';
                answer = x * y;
            }

            System.out.print(x+" "+sign+" "+y+" = ");
            z = keyboard.nextInt();          

            if(z==answer){
                System.out.println("Correct");
                counter++;                
            } else {
                System.out.println("Wrong");       
            }
        }
        System.out.println("You answered "+counter+" questions correctly");
    }
}

它确实编译!!!

Answer 1

您需要在if/else上执行if/else sign并相应调整answer:

if (sign == '+') {
    answer = x + y;
} else if (sign == '-') {
    answer = x - y;
} else if (sign == '*') {
    answer = x * y;
} else {
    System.err.println("Unknown operator: " + sign);
}

或者,您可以使用switch声明:

switch(sign) {
case('+'): 
    answer = x + y;
    break;
case('-'):
    answer = x - y;
    break;
case('*'):
    answer = x * y;
    break;
default:
    System.err.println("Unknown operator: " + sign);
    break;
}