package a;

import java.text.DecimalFormat;

public class bb {

  public static void main(String[] args) {                                         //实例化方法

         operation();

     }

     public static void operation() {

       

         for (int i = 1;  i<= 300; i++) {                                          //三百个

             int x =  (int) (Math.random() * 4);                                   //四个方法

             int a =  (int) (Math.random() * 100);                                 //a小于100

             int b =  (int) (Math.random() * 100);                                 //b小于100

             switch (x) {

             case 0:                                                               //加法

                 System.out.println(" ");

                 System.out.println(  i + ".  "+a + "+" + b + "=" + (a + b));

                 break;

             case 1:                                                               //减法

              System.out.println(" ");

                 System.out.println( i + ".  "+a + "-" + b + "=" + (a - b));

                 break;

             case 2:                                                               //乘法

              System.out.println(" ");

                 System.out.println(  i + ".  "+a + "*" + b + "=" + (a * b));

                 break;

             case 3:

                 if (b == 0) {                                                      //如果b=0从算

                     i--;

                     break;

                 } else {                                                           //如果是整数输出

                     if (a % b == 0) {

                      System.out.println(" ");

                        System.out.println( i + ".  "+a + "/" + b + "=" + (a / b));

                     } else {                                                       //如果是余数保留两位小数输出

                      System.out.println(" ");

                         double num = (double) a / b;

                         String ss = new DecimalFormat("0.00").format(num);

                         System.out.println( i + ".  "+a + "/" + b + "=" + ss);

                     }

                 }

                 break;

             default:                                                               //全部结束

                 break;

             }

         }

     }

}

                   运行结果