随机生成四则运算

首先完成生成随机数，包括随机生成几组数字，生成随机数的范围，四则运算符号等，要完成具体逻辑，进行加减乘除的分类，指定随机生成几组数字，然后再排列数字和四则运算符号。

这个四则运算还有很多不完善的地方，代码也不是最好的方法，敬请谅解。

下面是部分代码：

public class MainActivity extends AppCompatActivity {
    private int a,b,c,d,sy;
    private TextView textView;
    private Button btn_answer,btn_next;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView=(TextView)findViewById(R.id.textView);
        btn_answer = (Button)findViewById(R.id.btn_answer);
        btn_next = (Button)findViewById(R.id.btn_next);
        sz();
        sw();

        //点击显示按钮时显示答案
        btn_answer.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                switch (sy) {
                    case 0:
                        textView.setText(a + "+" + b + "=" + (a + b));
                        break;
                    case 1:
                        textView.setText(a + "-" + b + "=" + (a - b));
                        break;
                    case 2:
                        textView.setText(a + "+" + b +"*"+ c + "="+ (a+b*c));
                        break;
                    case 3:
                        textView.setText(a + "+" + b +"/"+ c + "="+(a+b/c));
                        break;
                    case 4:
                        textView.setText(a + "-" + b +"*"+ c + "="+(a-b*c));
                        break;
                    case 5:
                        textView.setText(a + "-" + b +"/"+ c + "="+(a-b/c));
                        break;
                    case 6:
                        textView.setText(a + "*" + b + "=" + (a*b));
                        break;
                    case 7:
                        textView.setText(a + "/" + b + "=" + (a/b));
                        break;
                }
            }
        });

        //点击下一题
        btn_next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                sz();
                sw();
            }
        });
    }

    //生成随机数
    private void sz(){
        Random random = new Random();
        random.nextInt();
        a = random.nextInt(100);
        b = random.nextInt(100);
        c = random.nextInt(100);
        sy = random.nextInt(8);
    }
    //显示题目
    private void sw(){
        switch (sy) {
            case 0:
                textView.setText(a + "*" + b + "+" + c + "-" + d + "=?");
                break;
            case 1:
                textView.setText(a + "*" + b + "/" + c + "+" + d + "=?");
                break;
            case 2:
                textView.setText(a + "*" + b + "-" + c + "+" + d + "=?");
                break;
            case 3:
                textView.setText(a + "/" + b + "*" + c + "+" + d + "=?");
                break;
        }
    }
}

运行截图：