Question

c#分别使用for、while、do-while循环计算1!+2!+...+20!阶乘的和

Answer 1

sum = 0;
for (i=1;i<=20;i++)
{
multiply = 1;
for (j=1;j<i;j++)
{
multiply = j*multiply;
}
sum += multiply;
}

Answer 2

//计算阶乘的私有方法

private int jiecheng(int i){
if(i==1)
return 1;
else
return i*jiecheng(i--);

}

//for
private int sumjiechengByFor(int n)
{
int sum =0;
for(int i=1;i<=n;i++)
{
sum +=jiecheng(i);

}
return sum;

}

//while
private int sumjiechengByWhile(int n)
{
int sum =0,i=1;
while(i<=n)
{
sum +=jiecheng(i);
i++;

}
return sum;
}

//dowhile
private int sumjiechengByDoWhile(int n)
{
int sum =0,i=1;
if(i<=0) return 0; //参数应该大于0

do
{

sum +=jiecheng(i);
i++;

}while(i<=n);

return sum;
}