4-2-2 多重循环-break跳出

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让程序输出100以内素数

import java.util.Scanner;public class Main {            public static void main(String[] args) {                          Scanner in = new Scanner(System.in);//    int n = in.nextInt();                for(int n = 2;n < 100; n++)    {    int isPrime = 1;    for (int i = 2; i < n ; i++ )        {        if(n % i == 0)        {        isPrime = 0;               break;        }        }        if( isPrime == 1)        {        System.out.print(n+" ");        }        else        {//        System.out.println(n+"不是素数");        }    }            }     }

错：

1、放在for循环之外，导致输出2 3

    int isPrime = 1;

注：

1、for里面还有for，叫做多重循环/嵌套循环

多重循环/嵌套循环

例1

        for ( int n1 = 0; n1<10 ; ++n1 )        {        for (int n2 = 0; n2 <50; ++n2)        {        System.out.println(n1+":"+n2);        }            }

例2（99乘法表）

        for ( int i = 1; i <= 9 ; i++ )        {        for (int j = 1; j <= 9; j++)        {        System.out.println("\t"+(i*j));        }                System.out.println();    }

里面的循环做更多次

输出前50素数的程序

1.不知道循环次数，for不合适

2.需要有一个数数器

留作作业

凑硬币（枚举，穷举）

import java.util.Scanner;public class Main {            public static void main(String[] args) {                          Scanner in = new Scanner(System.in);        int amount = in.nextInt();        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 + five*5+ten*10+twenty*20 == amount)            {            System.out.println(one+"张1圆，"+five+"张5圆，"+ten+"张5圆，"+twenty+"张20圆");            }            }            }            }        }                   }     }

如果只要一种

用break?麻烦，只能跳出一层循环

import java.util.Scanner;public class Main {            public static void main(String[] args) {                          Scanner in = new Scanner(System.in);        int amount = in.nextInt();                int isExit = 0;                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 + five*5+ten*10+twenty*20 == amount)            {            System.out.println(one+"张1圆，"+five+"张5圆，"+ten+"张5圆，"+twenty+"张20圆");            isExit = 1;            break;            }            }            if (isExit == 1)            {            break;            }            }            if (isExit == 1)        {        break;        }            }        if (isExit == 1)    {    break;    }        }    }     }

或者，加个标号

import java.util.Scanner;public class Main {            public static void main(String[] args) {                          Scanner in = new Scanner(System.in);        int amount = in.nextInt();                int isExit = 0;//        标号,命名下面那个for        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 + five*5+ten*10+twenty*20 == amount)            {            System.out.println(one+"张1圆，"+five+"张5圆，"+ten+"张5圆，"+twenty+"张20圆");            break OUT;            }            }            }            }        }                   }     }

1、break、continue都有用

2、起名任意

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