Question

求c++程序 输入n，输出：1!+2!+3!+...+n!

只能用if循环和for循环，i* 等不能使用

Answer 1

#include <iostream.h>
int main()
{
int i,j,n,p;
int s=0;
cout<<"n=";
cin>>n;
for(i=1;i<=n;i++)
{
p=1;
for(j=1;j<=i;j++)
{
p*=j;
}
s+=p;
}
cout<<"1!+2!+3!+...+n!="<<s<<endl;
return 0;
}

追问

能解释每步吗

Answer 2

#include <iostream>
using namespace std;
int main()
{
int fact(int n);

int n;
cout << "Input num N: " << endl;
cin >> n;
getchar();
int sum = 0;
int fac = 1;
for (int i = 1; i <= n; i++)
sum += fact(i);

cout << "1!+2!+..+" << n << "!=" << sum << endl;

getchar();

return 0;
}

int fact(int n)
{
if (n == 1 || n == 0)
return 1;
else
return n * fact(n - 1);
}

Answer 3

#include <stdio.h>
#include <iostream>
using namespace std;
int main()
{
cout << "请输入一个整数n"<<endl;
cin>>n;
int sum=0;
int fac=1;
for(int i=1;i<=n;i++)
{ fac=1;
for(int j=1;j<=i;j++)
{
fac*=j;
}
sum+=fac;
}
cout<<"1!+2!+..+"<<n<<"!=“<<sum<<endl;
return 0;
}

追问

fac*=j;
这一句不能用

追答

#include
#include
using namespace std;
int main()
{
cout >n;
int sum=0;

for(int i=1;i<=n;i++)
{
sum+=fac(i);
}
cout<<"1!+2!+..+"<<n<<"!=“<<sum<<endl;
return 0;
}
int fac(int n)
{
if(n==1||n==0)
return 1;
else
return fac(n-1);
}

Answer 4

if where you doing