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  • Java错误1(2015-8-27)

    1、

    public class FourTest{

     public static void main(String[] args){  

                  long sum = 0;  

                  long jc_sum = 1;//该处必须是long数据类型。如果是int,jc_sum=20!的话,会丢失精度。都必须是long数据类型。

                  for(int i=1;i<=20;i++){    

                               for(int j=1;j<=i;j++){    

                                             jc_sum = jc_sum*j;   

                               }   

                                sum = sum + jc_sum;     //将jc_sum=n!的值赋值给sum.

                                jc_sum = 1;     //然后必须要将jc_sum赋值为1.

                   }  

                   System.out.println("sum:"+sum);

     } }

    2、

    public class Test3{    

        public static void main(String [] args{                                                         

                   long sum=0;           

                   long jc=1;

                   for(int i=1;i<=20;i++){                 

                                  for(int j=1;j<=i;j++){                 

                                                    jc=jc*j;                                                

                                   }              

                                  sum=sum+jc;             

                                  jc=1;//-----------关键点,重新赋值1。否则计算结果不对。        

                   }                                   

                    System.out.println("求1!+2!+3!+...+20!之和是:"+sum);

    }}

    3、

    public class Test33{      

      public static void main(String[] args){           

                       System.out.println("1!+2!+3!+……+20!="+getSum(20));     

       }        

       public static long getSum(int n){           

                        long fac=1;          

                        long sum=0;        

                        for(int i=1;i<=n;i++){                     

                                       for(int k=1;k<=i;k++){                  

                                                         fac=fac*k;               

                                        }                                      

                                       sum=sum+fac;                    

                                       fac=1;              

                        }           

                        return sum;

    } }

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  • 原文地址:https://www.cnblogs.com/Ly426/p/4763426.html
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