4.2上机练习

1. 打印出所有的"水仙花数"，所谓"水仙花数"是指一个三位数，其各位数字立方和等于该数本身。例如：153是一个"水仙花数"，因为153=1的三次方＋5的三次方＋3的三次方。（知识点：循环语句、条件语句）

package chap1;

public class Main
{
    public static void main(String[] args)
    {
        for (int i = 100; i < 1000; i++)
        {
            int bai = i / 100;
            int shi = i / 10 % 10;
            int ge = i % 10;
            if (Math.pow(bai, 3) + Math.pow(shi, 3) + Math.pow(ge, 3) == i)
            {
                System.out.println(i);
            }
        }
    }
}

　　

2.在控制台输出以下图形（知识点：循环语句、条件语句）

package chap1;

public class Main
{
    public static void main(String[] args)
    {
        for (int i = 0; i < 6; i++)
        {
            for (int j = 1; j <= i + 1; j++)
            {
                System.out.print(j);
            }
            System.out.println();
        }
        System.out.println();
        for (int i = 6; i >= 1; i--)
        {
            for (int j = 1; j <= i; j++)
            {
                System.out.print(j);
            }
            System.out.println();
        }
        System.out.println();
        for (int i = 0; i < 6; i++)
        {
            for (int j = 5; j > i; j--)
            {
                System.out.print(" ");
            }
            for (int j = 1; j <= i + 1; j++)
            {
                System.out.print(j);
            }
            System.out.println();
        }
        System.out.println();
        for (int i = 0; i < 6; i++)
        {
            for (int j = 0; j < i; j++)
            {
                System.out.print(" ");
            }
            for (int j = 1; j <= 6 - i; j++)
            {
                System.out.print(j);
            }
            System.out.println();
        }
    }
}

　　

3. 输入年月日，判断这是这一年中的第几天（知识点：循环语句、条件语句）

package chap1;

import java.util.Scanner;

public class Main
{
    public static void main(String[] args)
    {
        Scanner s = new Scanner(System.in);
        System.out.println("请依次输入年月日:");
        int nian = s.nextInt();
        int yue = s.nextInt();
        int ri = s.nextInt();
        int days = 0;
        switch (yue)
        {
            case 1:
                days = 0;
                break;
            case 2:
                days = 31;
                break;
            case 3:
                days = 59;
                break;
            case 4:
                days = 90;
                break;
            case 5:
                days = 120;
                break;
            case 6:
                days = 151;
                break;
            case 7:
                days = 181;
                break;
            case 8:
                days = 212;
                break;
            case 9:
                days = 243;
                break;
            case 10:
                days = 273;
                break;
            case 11:
                days = 304;
                break;
            case 12:
                days = 334;
                break;
            default:
                System.out.println("年份错误");
                return;
        }
        if (nian % 4 == 0 && nian % 100 != 0 || nian % 400 == 0)
        {
            if (yue > 2)
            {
                days ++;
            }
        }
        System.out.println("这是" + nian + "年的第" + (days + ri) + "天");
    }
}

　　

　　

4．由控制台输入一个4位整数，求将该数反转以后的数，如原数为1234，反转后的数位4321（知识点：循环语句、条件语句）

package chap1;

import java.util.Scanner;

public class Main
{
    public static void main(String[] args)
    {
        Scanner s = new Scanner(System.in);
        System.out.println("请输入一个四位数:");
        int num = s.nextInt();
        int ge = num % 10;
        int shi = num / 10 % 10;
        int bai = num / 100 % 10;
        int qian = num / 1000;
        System.out.println("反转后结果为:" + ge + shi + bai + qian);
    }
}