JAVA基础学习（3）之循环

3循环

• 3.1循环
  • 3.1.1循环
    • 一直要做的行为进行循环
  • 3.1.2数数字
    • while(){}判断是否进行
    • 数数字：number/10

    •  //数数字
      Scanner in = new Scanner(System.in);
               System.out.println("请输入一个数！");
               int number = in.nextInt();
               int count = 0;
               while (number > 0)
               {
                   number = number / 10;
                   count++;
                   System.out.println("number=" + number + " count=" + count);
               }
               System.out.println("该数有" + count + "位！");

  • 3.1.3while循环
    • 测试数据
      • 个位数
      • 10
      • 0
      • 负数

      •  Scanner in = new Scanner(System.in);//解决0的数数字
                 System.out.println("请输入一个数！");
                 int number = in.nextInt();
                 int count = 0;
                 do
                 {
                     number = number / 10;
                     count++;
                     System.out.println("number:" + number + " count:" + count);
                 } while (number > 0);
                 System.out.println("该数有" + count + "位");

  • 3.1.4do-while循环
    • while();分号不能忘记

    • //计数循环
      Scanner in = new Scanner(System.in);
              int count = 100;
              do
              {
                  System.out.println(count);
                  count = count - 1;
              } while (count > 0);
              System.out.println(count);
              System.out.println("发射!");

• 3.2循环的例子
  • 计数循环
    • 如果要模拟运行一个很大次数的循环，可以模拟较少的循环次数，然后作出判断。
  • 算平均数
    • 　　

       Scanner in = new Scanner(System.in);//计算平均数
               int number;
               int sum = 0;
               int count = 0;
               while ((number = in.nextInt()) != -1)
               {
                   sum = sum + number;
                   count++;
               }
               if (count > 0)
               {
                   System.out.println("平均数为：" + (double) sum / count);
      
               }

  • 猜数
    • 　　

       Scanner in = new Scanner(System.in);//猜数游戏
               int number = (int) (Math.random() * 100 + 1);// [0,1)-->[0,100)-->[1,100]
               int a;
               int count = 0;
               while ((a = in.nextInt()) != number)
               {
                   if (a > number)
                   {
                       System.out.println("大了");
                   } else if (a < number)
                   {
                       System.out.println("小了");
                   }
                   count++;
               }
               System.out.println("恭喜你猜对了,你猜了" + count + "次！");

  • 整数分解

    •  Scanner in = new Scanner(System.in);//整数分解
               int number;
               number = in.nextInt();
               int result = 0;
               do
               {
                   int digit = number % 10;
                   result = result * 10 + digit;
                   System.out.print(digit);
                   number = number / 10;
               } while (number > 0);
               System.out.println();
               System.out.println(result);

    • n%10->得到个位
    • n/10->去掉一位