java中 9+99+999+……+9999999999的代码

package d7_8;import java.util.Arrays;public class Zuoye_9 { public static void main(String[] args) {  long []arr={};  long sum=0;  for(int i=0;i<10;i++){   arr=Arrays.copyOf(arr, arr.length+1);      arr[i]=(long) (Math.pow(10, i+1)-1);   sum+=arr[i];         if(i==9){       System.out.print(arr[i]);      }else{       System.out.print(arr[i]+'+');      }          }  System.out.print('='+sum); }}

Scanner sc=new Scanner(System.in);  System.out.println('请输入大于等于2的整数：');  double sum = 0;  int j=sc.nextInt();  for(int  i=1;i<=j;i++){   double k=(double) i;   sum+=1/k;    if(i==j){     System.out.println('1'+'/'+i+'='+sum);    }else{     System.out.print('1'+'/'+i+'+');    }     }   }}

package d7_8;import java.util.Scanner;public class Zuoye_10 { public static void main(String[] args) {  Scanner sc=new Scanner(System.in);  System.out.println('请输入大于等于2的整数：');  double sum = 0;  int j=sc.nextInt();  for(int  i=1;i<=j;i++){   double k=(double) i;   sum+=1/k;    if(i==j){     System.out.println('1'+'/'+i+'='+sum);    }else{     System.out.print('1'+'/'+i+'+');    }     }   }}

九九乘法表：

package d7_8;public class Sheet { public static void main(String[] args) {  for(int i=1;i<=9;i++){   for(int j=1;j<=i;j++){    System.out.print(i+'*'+j+'='+i*j+'\t');   }   System.out.println();  } }}