Java语言：使用While循环计算1+1/2!+1/3!+........+1/20!

Answer 1

package com.haimian;public class Hello {//main方法； public static void main(String[] args) { int num=3; Hello hello=new Hello(); System.out.println(hello.function(num)); } public double function(int num){ double i=1; double count=0; while(i<num){ count=count+1/i; i=i+1;} return count; }}

Answer 2

public class WhilePractice {/**  * 计算1+1/2!+......+1/20!  */ public static void main(String[] args) {  int i = 1,j=1;  double sum =0;  while (i<=20) {   j = j*i;            //做阶乘（1~20）   sum = sum+(1.0)/j;   //定义sum为double类型，用1.0除以j   i++;}System.out.println(sum); }} 

Answer 3

public class aaa{ public static void main(String args[]){ double ans = 0; long i, sum; i = 1; sum = 1; while(i < 20){ i++; sum *= i; System.out.println(sum); ans += 1.0*i/sum; } System.out.println(ans); } }如果计算到21!的话，long类型的数会溢出