4.2

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 learn;

public class day05 {
    public static void main(String[] args) {
        for(int i=100;i<1000;i++) {
            int ge=i%10;
            int shi=i/10%10;
            int bai=i/100;
            if(ge*ge*ge+shi*shi*shi+bai*bai*bai==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 learn;

public class day05 {
    public static void main(String[] args) {
        for(int i=1;i<7;i++) {
            for(int j=1;j<=i;j++) {
                System.out.print(j);
            }
            System.out.println();
        }
    }
}

package learn;

public class day05 {
    public static void main(String[] args) {
        for(int i=1;i<7;i++) {
            for(int j=1;j<=7-i;j++) {
                System.out.print(j);
            }
            System.out.println();
        }
    }
}

package learn;

public class day05 {
    public static void main(String[] args) {
        for(int i=1;i<7;i++) {
            for(int j=i;j>0;j--) {
                System.out.print(j);
            }
            System.out.println();
        }
    }
}

package learn;

public class day05 {
    public static void main(String[] args) {
        for(int i=6;i>0;i--) {
            for(int k=0;k<6-i;k++) {
                System.out.print(" ");
            }
            for(int j=1;j<=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 learn;

import java.util.Scanner;

public class day05 {
    public static void main(String[] args) {
        int x = 0;
        Scanner sc=new Scanner(System.in);
        System.out.print("请输入年份");
        int year=sc.nextInt();
        System.out.print("请输入月份");
        int month=sc.nextInt();
        System.out.print("请输入日期");
        int date= sc.nextInt();
        if(year%4==0 && year%100!=0 || year%400==0) {
            switch(month) {
            case 1:  x=31; break;
            case 2:  x=31+29;break;
            case 3:  x=31+29+31;break;
            case 4:  x=31+29+31+30;break;
            case 5:  x=31+29+31+30+31;break;
            case 6:  x=31+29+31+30+31+30;break;
            case 7:  x=31+29+31+30+31+30+31;break;
            case 8:  x=31+29+31+30+31+30+31+31;break;
            case 9:  x=31+29+31+30+31+30+31+31+30;break;
            case 10: x=31+29+31+30+31+30+31+31+30+31;break;
            case 11: x=31+29+31+30+31+30+31+31+30+31+30;break;
            case 12: x=31+29+31+30+31+30+31+31+30+31+30+31;break;
            }
        }else {
            switch(month) {
            case 1:  x=31;break;
            case 2:  x=31+28;break;
            case 3:  x=31+28+31;break;
            case 4:  x=31+28+31+30;break;
            case 5:  x=31+28+31+30+31;break;
            case 6:  x=31+28+31+30+31+30;break;
            case 7:  x=31+28+31+30+31+30+31;break;
            case 8:  x=31+28+31+30+31+30+31+31;break;
            case 9:  x=31+28+31+30+31+30+31+31+30;break;
            case 10: x=31+28+31+30+31+30+31+31+30+31;break;
            case 11: x=31+28+31+30+31+30+31+31+30+31+30;break;
            case 12: x=31+28+31+30+31+30+31+31+30+31+30+31;break;
            }
        }
        System.out.println(year+"年"+month+"月"+date+"日"+"是第"+(x+date)+"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 learn;

import java.util.Scanner;

public class day05 {
    public static void main(String[] args) {
    Scanner sc=new Scanner(System.in);
    System.out.println("请输入一个四位数");
    int num=sc.nextInt();
    int qian=num/1000;
    int bai=num/100%10;
    int shi=num/10%10;
    int ge=num%10;
    System.out.println("原先的数为："+num+"现在的为"+(qian+bai*10+shi*100+ge*1000));    
    }
}