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);

巴特西

JAVA基础学习（4）之循环控制

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