分别用do-while循环和for循环计算1+1/2!+1/3!+1/4!+…的前20项和

 public class demo49_4_3 {
 
public  static   void  main(String[] args) {
double sum=0,item=1;
int i=1;
 
//for循环计算
for(;i<=20;) {
sum = sum+item;
i=i+1;
item = item*(1.0/i);
}
 
//do-while循环计算
do {
sum = sum+item;
i=i+1;
item = item*(1.0/i);
}while(i<=20);

System.out.println(sum);
 
}
 
}  

结果为：
1.7182818284590455

用for循环计算8+88+888+…前10项之和

 public class demo49_4_5 {
 
public static void main(String[] args) {
long sum=0,item=8;
for(int i=1;i<=10;i++) {
sum = sum+item;
item = item*10+8;
}
System.out.println(sum);
 
}
 
}  

结果为：

9876543200