int sum=0;
for(int j=1;j<=15;j++) {
sum+=f(j); }
System.out.println(sum); } }
14．编写程序，分别用do-while和for循环计算1+1/2!+1/3!+1/4!+…的前15项的和。
for循环代码:
public class For_FactorialSum {
static int f(int x) {
if (x<=0) return 1; else
return x*f(x-1);
}
public static void main(String[]args){
double sum=0;
for(int j=1;j<=15;j++) {
sum+=1.0/f(j); }
System.out.println(sum); } }
do-while循环代码:
public class DoWhile_FactorialSum {
static int f(int x) {
if (x<=0) return 1; else
return x*f(x-1); }
public static void main(String[]args){
double sum=0; int j=1; do {
sum+=1.0/f(j); j++; }
while(j<=15);
System.out.println(sum); } }
15．编写一个程序，用选择法对数组a[]={20,10,55,40,30,70,60,80,90,100}进行从大到小的排序。
(分别采用冒泡排序、选择排序和插入排序方法)
public class SortAll {
public static void main(String[] args) {
int a[]={20,10,55,40,30,70,60,80,90,100};
System.out.println(―—-冒泡排序的结果：―);
maoPao(a);
System.out.println();
System.out.println(―—-选择排序的结果：―);
xuanZe(a);
System.out.println();
System.out.println(―—-插入排序的结果：―);
chaRu(a); }
// 冒泡排序
public static void maoPao(int[] x) {
for (int i = 0; i < x.length; i++) {
for (int j = i + 1; j < x.length; j++) {
if (x[i] > x[j]) {
int temp = x[i];
x[i] = x[j];
x[j] = temp; } } }
for (int i : x) {
System.out.print(i + ‖ ‖); } }
// 选择排序
public static void xuanZe(int[] x) {
for (int i = 0; i < x.length; i++) {