课堂练习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 calsswork;
import java.util.Scanner;
public class text1 {
    public static void main(String[] args) {
            for (int i = 100; i <= 999; i++) {
                int ge = i % 10;
                int shi = (i/10) % 10;
                int bai = (i/100) % 10;
                int sum = ge*ge*ge + shi*shi*shi + bai*bai*bai; 
                if (sum == 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 calsswork;
import java.util.Scanner;
public class text1 {
    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 calsswork;
import java.util.Scanner;
public class text1 {
    public static void main(String[] args) {
        for(int i=6;i>=0;i--) {
            for(int j=1;j<=i;j++) {
                System.out.print(j);
            }
            System.out.println();
        }
    }
}

package calsswork;
import java.util.Scanner;
public class text1 {
 public static void main(String[] args) {
            System.out.println("     1
    21
   321
  4321
 54321
654321");
        }
    }

package calsswork;
import java.util.Scanner;
public class text1 {
    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 calsswork;
import java.util.Scanner;
public class text1 {
    public static void main(String[] args) {
          int year,mouth,days;
            int day = 0;
            int a = 0; 
            int b = 0;
            Scanner scanner = new Scanner(System.in);
            do {
                System.out.println("输入年:");
                year = scanner.nextInt();
                System.out.println("输入月:");
                mouth = scanner.nextInt();
                System.out.println("输入日:");
                days = scanner.nextInt();
                if (year < 0 || mouth < 0 || mouth > 12 || days < 0 || days > 31) {
                    System.out.println("输入错误请重新输入!");
                    b = 1;
                }
            } while (b == 1);
            
            for (int i = 1; i < mouth; i++) {
                switch (i) {
                case 1:
                case 3:
                case 5:
                case 7:
                case 8:
                case 10:
                case 12: {
                    day = 31;
                    break;
                }
                case 4:
                case 6:
                case 9:
                case 11: {
                    day = 30;
                    break;
                }
                case 2: {
                    if ((year % 100 != 0 && year % 4 == 0) || (year % 100 == 0 && year % 400 == 0)) {
                        day = 29;
                    } else {
                        day = 28;
                    }
                }
                default:
                    break;
                }
                a += day;
            }
            System.out.println("这是" + year + "年的" + (a + days) + "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 calsswork;
import java.util.Scanner;
public class text1 {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        System.out.println("输入四位数字");
        int n=sc.nextInt(); 
        int ge = n / 1000; 
        int shi = n / 100 % 10; 
        int bai = n / 10 % 10; 
        int qian = n % 10; 
        int s = qian * 1000 + bai * 100 + shi * 10 + ge; 
        System.out.println("反转后=" + s); 
    }
}