JAVA基础学习（4）之循环控制

4循环控制

• 4.1 for循环
  • 4.1.1 for循环
    • 固定次数for循环
    • 先执行一次do-while循环
    • 其他while循环

    • Scanner in = new Scanner(System.in);//计算阶乘
              int n = in.nextInt();
              int factor = 1;
              ;
              for (int i = 1; i <= n; i++)
              {
      //            factor=i*factor;
                  factor *= factor;
              }
              System.out.println(n + "的阶乘值为：" + factor);

  • 4.1.2 复合赋值
    • a*=6 -> a=a*6
    • a/=b+6 -> a=a/(b*6)
    • i=i+1 ->i i++

    •  Scanner in = new Scanner(System.in);//判断素数
               int n = in.nextInt();
               int flag = 0;
               for (int i = 2; i < n; i++)
               {
                   if (n % i == 0)
                   {
                       flag = 1;
                       break;
                   }
               }
               if (flag == 1)
               {
                   System.out.println(n + "不是素数!");
               } else
               {
                   System.out.println(n + "是素数！");
               }

• 4.2循环控制
  • 4.2.1循环控制
    • 素数判断

    •  for (int n = 2; n < 100; n++)//输出100以内的素数
               {
                   int flag = 1;
                   for (int i = 2; i < n; i++)
                   {
                       if (n % i == 0)
                       {
                           flag = 0;
                           break;
                       }
                   }
                   if (flag == 1)
                   {
                       System.out.print(n + " ");
                   }
               }

    • break跳出循环
    • continue跳出循环这一轮的语句进入下一轮
  • 4.2.2多重循环
    • lable：
    • 标号标示循环，break lable或 continue lable 可以跳出

    •                  int count = 1;//输出前59个素数
               int n = 2;
               while (count <= 50)
               {
                   int flag = 1;
                   for (int i = 2; i < n; i++)
                   {
                       if (n % i == 0)
                       {
                           flag = 0;
                           break;
                       }
                   }
                   if (flag == 1)
                   {
                       System.out.println("第" + count + "个素数：" + n);
                       count++;
                   }
                   n++;
               }                

  • 4.2.3逻辑类型
    • 按照优先级排列
    • ！
    • &&
    • ||
    • 　

       Scanner in = new Scanner(System.in);//凑硬币
               int amount = in.nextInt();
               OUT: for (int one = 0; one <= amount; one++)
               {
                   for (int five = 0; five <= amount / 5; five++)
                   {
                       for (int ten = 0; ten <= amount / 10; ten++)
                       {
                           for (int twenty = 0; twenty <= amount / 20; twenty++)
                           {
                               if ((one + 5 * five + 10 * ten + 20 * twenty) == amount)
                               {
                                   System.out.println(one + "张1元，" + five + "张5元，" + ten + "张10元，" + twenty + "张20元");
                                   break OUT;
                               }
                           }
                       }
                   }
               }

    • 
• 4.3循环的例子
  • 4.3.1求和
    • 　　

       Scanner in = new Scanner(System.in);// f=1-1/2+1/3...求和
               int n = in.nextInt();
               double sum=0;
               int sign=1;
               for (int i = 1; i <= n; i++,sign=-sign)
               {
                   sum+=sign*1.0/i;
               }
               System.out.println("和为："+sum);
               System.out.print("和为：");
               System.out.printf("%.2f",sum);

  • 4.3.2最大公约数
    • 　　

       Scanner in=new Scanner(System.in);//求最大公约数
               int a=in.nextInt();
               int b=in.nextInt();
               int gcd=1;
       //        for(int i=2;i<=a&&i<=b;i++)
               for (int i = 2; i <= (a<b?a:b); i++)
               {
                   if((a%i==0)&&(b%i==0))
                   {
                       gcd=i;
                   }
               }
               System.out.println(a+"和"+b+"最大公约数为:"+gcd);

    •  Scanner in=new Scanner(System.in);//辗转相除法求最大公约数
               System.out.println("请输入a和b：");
               int a=in.nextInt();
               int b=in.nextInt();
      
               while (b!=0)
               {
                   int r=a%b;
                   System.out.println(a+" "+b+" "+r);
                   a=b;
                   b=r;
               }
               System.out.println("最大的公约数为："+a);