自动生成小学四则运算程序

import java.lang.*;
import java.util.Scanner;

public class Kq {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int a, b, c;
        int systemanswer = 0;
        int useranswer = 0;
        int rightnumber = 0;
        char op = 0;
        System.out.println("欢迎使用自动生成小学四则运算程序，本程序每一次出十道题，用户做对6题或6题以上即退出程序");
        do {
            for (int i = 1; i <= 10; i++) {
                a = 1 + (int) (Math.random() * 10);
                b = 1 + (int) (Math.random() * 10);
                c = 1 + (int) (Math.random() * 4);
                switch (c) {
                case 1:
                    op = '+';
                    systemanswer = a + b;
                    break;
                case 2:
                    op = '-';
                    systemanswer = a - b;
                    break;
                case 3:
                    op = '*';
                    systemanswer = a * b;
                    break;
                case 4:
                    op = '/';
                    systemanswer = a / b;
                    break;
                default:
                    System.out.printf("无效");
                }
                System.out.printf("%d%c%d=?
", a, op, b);
                Scanner in = new Scanner(System.in);
                useranswer = in.nextInt();
                if (useranswer == systemanswer) {
                    System.out.printf("right!
");
                    rightnumber++;
                } else {
                    System.out.printf("wrong!
");
                }
            }
            System.out.printf("总分%d
", rightnumber * 10);
            System.out.printf("百分比%d%%
", rightnumber * 10);
            if (rightnumber * 10 < 60) {
                System.out.printf("再来一遍
");
                rightnumber = 0;
            }
        } while (rightnumber * 10 < 60);

    }

}