四则运算升级2

import java.util.*;
public class First {
      public static void main (String[] agrs){
          double a,b,c,d;
          int count1=0,count2=0;
          int i;
          String[] s={"+","-","*","/"};
          Scanner sc=new Scanner(System.in);
              int op= 0;
              while(true){
               System.out.println("选择功能：\n0.退出1.简单的加减乘除运算 2.复合运算 3.含真分数运算");
               op= sc.nextInt();
               if (0 == op) {break;}
               if (1 == op) {
                   System.out.println("(5分/道)请输入题目数目：");
                   int n=sc.nextInt();
                   System.out.print("请输入算数的范围(由小到大)：");
                   int min=sc.nextInt();
                   int max=sc.nextInt();
                   if(min>max){
                       System.out.print("输入出错");
                       break;
                   }
                   Random r= new Random();
                      for(i=0;i<n;i++){
                          a=r.nextInt(max)%(max-min+1) + min;
                          b=r.nextInt(max)%(max-min+1) + min;
                         int l= r.nextInt(s.length);//随机数，小于数组的长度数, 0~3
                         System.out.print(a+s[l]+b); //打印随机字符
                         System.out.print("=");
                            double A=sc.nextDouble();
                            if("+"==s[l]){
                                if(A==a+b){
                                    System.out.println("this is right!");
                                    count1++;
                                }
                                else {
                                   System.out.println("this is wroing!"+"正确答案是:"+(a+b));
                                   count2++;
                                   }
                         }
                         else if("-"==s[l]){
                             if((a-b)>-11){
                                    if(A==a-b){
                                        System.out.println("this is right!");
                                        count1++;
                                    }
                                    else {
                                       System.out.println("this is wroing!"+"正确答案是:"+(a-b));
                                       count2++;
                                       }
                             }
                             else{
                                 a=r.nextInt(max)%(max-min+1) + min;
                                 b=r.nextInt(max)%(max-min+1) + min;
                                 if(A==a-b){
                                     System.out.println("this is right!");
                                     count1++;
                                 }
                                 else {
                                 System.out.println("this is wroing!"+"正确答案是:"+(a-b));
                                 count2++;
                                 }
                             }
                            }
                         else if("*"==s[l]){
                             if(A==a*b){
                                    System.out.println("this is right!");
                                    count1++;
                                }
                             else {
                                    System.out.println("this is wroing!"+"正确答案是:"+(a*b));
                                    count2++;
                                }
                         }
                         else if("/"==s[l]){
                             if(A==a/b){
                                    System.out.println("this is right!");
                                    count1++;
                                }
                             else {
                                  System.out.println("this is wroing!"+"正确答案是:"+String.format("%.2f",a/b));
                                  count2++;
                                }
                         }
                      }
                      System.out.println("此题对了:"+count1+" "+"错了:"+count2+" "+"得分为:"+5*count1);
               }
               else if (2 == op) {}
               else if (3 == op) {
                   //分子
                   int q,p;
                   //分母
                   int y,w;
                   System.out.println("(5分/道)请输入题目数目：");
                   int n=sc.nextInt();
                   System.out.print("请输入算数的范围(由小到大)：");
                   int min=sc.nextInt();
                   int max=sc.nextInt();
                   if(min>max){
                       System.out.print("输入出错");
                       break;
                   }
                   Random r= new Random();
                      for(i=0;i<n;i++){
                          q=r.nextInt(max)%(max-min+1) + min;
                          p=r.nextInt(max)%(max-min+1) + min;
                          y=r.nextInt(max)%(max-min+1) + min;
                          w=r.nextInt(max)%(max-min+1) + min;
                         int l= r.nextInt(s.length);//随机数，小于数组的长度数, 0~3
                         if((q<y && y!=0)||(p<w && w!=0)){
                             System.out.println(q+"/"+y+s[l]+p+"/"+w); //打印随机字符
                            System.out.print("=");
                                double A=sc.nextDouble();
                         }
                     }
               }
               else{
                   System.out.println("输入有误，请重新输入；");
               }
              }

      }
}

一开始，看到题目就开始做，没有详细的规划好，考虑自己的思路，想清楚需要定义几个类来实现功能，结果我所有的代码都在主函数里面了，导致我后来我越写越乱，错误百出，这样严重的养成了坏习惯。所以我决定还是放慢我的脚步，不在一味地追求能运行出结果就好了。我要学会如何运用类来编写我的程序，望老师指导，谢谢！