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++

 1 Scanner in = new Scanner(System.in);//判断素数
 2         int n = in.nextInt();
 3         int flag = 0;
 4         for (int i = 2; i < n; i++)
 5         {
 6             if (n % i == 0)
 7             {
 8                 flag = 1;
 9                 break;
10             }
11         }
12         if (flag == 1)
13         {
14             System.out.println(n + "不是素数!");
15         } else
16         {
17             System.out.println(n + "是素数！");
18         }

4.2循环控制

4.2.1循环控制

素数判断

 1 for (int n = 2; n < 100; n++)//输出100以内的素数
 2         {
 3             int flag = 1;
 4             for (int i = 2; i < n; i++)
 5             {
 6                 if (n % i == 0)
 7                 {
 8                     flag = 0;
 9                     break;
10                 }
11             }
12             if (flag == 1)
13             {
14                 System.out.print(n + " ");
15             }
16         }

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

 1                 int count = 1;//输出前59个素数
 2         int n = 2;
 3         while (count <= 50)
 4         {
 5             int flag = 1;
 6             for (int i = 2; i < n; i++)
 7             {
 8                 if (n % i == 0)
 9                 {
10                     flag = 0;
11                     break;
12                 }
13             }
14             if (flag == 1)
15             {
16                 System.out.println("第" + count + "个素数：" + n);
17                 count++;
18             }
19             n++;
20         }

4.2.3逻辑类型

按照优先级排列
！
&&
||

 1 Scanner in = new Scanner(System.in);//凑硬币
 2         int amount = in.nextInt();
 3         OUT: for (int one = 0; one <= amount; one++)
 4         {
 5             for (int five = 0; five <= amount / 5; five++)
 6             {
 7                 for (int ten = 0; ten <= amount / 10; ten++)
 8                 {
 9                     for (int twenty = 0; twenty <= amount / 20; twenty++)
10                     {
11                         if ((one + 5 * five + 10 * ten + 20 * twenty) == amount)
12                         {
13                             System.out.println(one + "张1元，" + five + "张5元，" + ten + "张10元，" + twenty + "张20元");
14                             break OUT;
15                         }
16                     }
17                 }
18             }
19         }

4.3循环的例子

4.3.1求和

 1 Scanner in = new Scanner(System.in);// f=1-1/2+1/3...求和
 2         int n = in.nextInt();
 3         double sum=0;
 4         int sign=1;
 5         for (int i = 1; i <= n; i++,sign=-sign)
 6         {
 7             sum+=sign*1.0/i;
 8         }
 9         System.out.println("和为："+sum);
10         System.out.print("和为：");
11         System.out.printf("%.2f",sum);

4.3.2最大公约数

 1 Scanner in=new Scanner(System.in);//求最大公约数
 2         int a=in.nextInt();
 3         int b=in.nextInt();
 4         int gcd=1;
 5 //        for(int i=2;i<=a&&i<=b;i++)
 6         for (int i = 2; i <= (a<b?a:b); i++)
 7         {
 8             if((a%i==0)&&(b%i==0))
 9             {
10                 gcd=i;
11             }
12         }
13         System.out.println(a+"和"+b+"最大公约数为:"+gcd);

 1 Scanner in=new Scanner(System.in);//辗转相除法求最大公约数
 2         System.out.println("请输入a和b：");
 3         int a=in.nextInt();
 4         int b=in.nextInt();
 5         
 6         while (b!=0)
 7         {
 8             int r=a%b;
 9             System.out.println(a+" "+b+" "+r);
10             a=b;
11             b=r;
12         }
13         System.out.println("最大的公约数为："+a);

posted on 2019-12-05 09:25 生长的力量阅读(336) 评论(0) 编辑收藏举报