#include  <iostream>
using namespace std; 


int main(int argc, char* argv[]) 
{ 
    int n = 5;
    int i, result = 0;
    for (i = n ; i >= 1; --i)
        result = (result + 1)*i;
    cout << result << endl;
    return 0; 
} 

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

int sum = 0; 
for (int i = 1; i <= 10; i++) 
{ 
int mul = 1; 
for (int j = i; j >= 1; j--) 
{ 
mul *= j; 
} 
sum += mul; 
} 
cout << sum << endl; 
}

#include <iostream>
using namespace std; 
long fac(int n) 
{ 
   if(n==1)  return 1; 
   else      return n*fac(n-1); 
} 

void main() 
{ 
  long int sum=0; 
  int num;
  cout<<"请输入你要计算的n的值：";
  cin>>num;
  for(int i=1;i <=num;i++) 
    sum+=fac(i); 
   cout <<sum <<endl; 
}

#include <iostream>
#include <stdlib.h>
using namespace std;
void main()
{
    int res=0;
    int n=4;
    int mid=1;
    for(int i=1;i<=n;i++)
    {
        res+=(mid=mid*i);
    }
    cout<<res<<endl;
}

#include <stdio.h>
#include <string.h>
#define MAX   20000
int fac(int n,char value[],int m)//计算n的阶层
{
    int   carry = 0; 
    int   r;
    int   valueLen = 1, index = 0;//valueLen为结果的长度
    int   i, j;
    //初始化value数组
    value[0] = '1';
    for (i = 1; i < m; i++)
    {
       value[i] = '0';
    }
    for(i = 1; i <= n; i++)
    {
       index = 0;
       for(j = 0; j < valueLen; j++)
       {
           r = (value[index] - '0')*i + carry;
        value[index] = r % 10 + '0';
        carry = r / 10;      //进位
        index++;
        if(carry > 0 && index == valueLen)//最高位有进位才能将长度加１
        {
           valueLen++;
        }
    
       } 
    }
    return valueLen;
}
void add(char *num1, char *num2)//大数相加
{
 int iLen1;
 int iLen2;
 int iTemp = 0;
 int i;

 iLen1 = strlen(num1);
 iLen2 = strlen(num2);

 memmove(num1+(100-iLen1), num1, iLen1);
 memset(num1, '0', 100-iLen1);
 memmove(num2+(100-iLen2), num2, iLen2);
 memset(num2, '0', 100-iLen2);

 for(i=99;i>=0; i--)
 {
  iTemp = (num1[i] - '0' + num2[i] - '0') + iTemp;

  num1[i] = (iTemp%10) + '0';

  iTemp = iTemp/10;
 }

 for(i=0; i<100; i++)
 {
  if(num1[i] != '0')break;
 }

 memmove(num1, num1+i, 100 - i);
 num1[100 - i] = '\0';
}

int test(char *num1)
{
 int iLen;
 int i;

 iLen = strlen(num1) -1;

 for(i=0; i<=iLen; i++)
 {
  if(num1[i] != num1[iLen-i])
  {
   return 1;
  }
 }

 return 0;
}


int main()
{
    char value[MAX];
    char sum[MAX];
    sum[0] = '1';
    for (int ti = 1; ti < MAX; ti++)
    {
    sum[ti] = '0';
    }
    int n=0;
    printf("Please input a factorial numble:");
    scanf("%d",&n);
    int valueLen=fac(n,value,MAX);

    for(int i =valueLen-1; i >= 0; i--)
    {
    printf("%c",value[i]);
    }
    printf("\n");

    return 0;
}

result = (result + 1)*i;

    for (i = n ; i >= 1; --i)
        result=(result + 1)*i;

    for(int i=1;i<=n;i++)
        res+=(mid=mid*i);

//calculate 1! + 2! + ... + n! where n is a positive integer

#include <iostream>
using namespace std;
const long maxlen = 100000;

int main()
{
    cout << "Input n: ";
    int n = 0;
    cin >> n;
    cout << "1! + 2! + ... + " << n << "! = ";
    
    int result[maxlen] = {0}, len_r = 0;
    int temp[maxlen] = {0}, len_t = 0;
    
    temp[0] = 1;
    len_t = 1;
    
    for (int x = 1; x <= n; x++)
    {
        temp[0] = temp[0] * x;
        for (int j = 1; j < len_t; j++)
        {
            temp[j] = temp[j] * x + temp[j-1] / 10;
            temp[j-1] = temp[j-1] % 10;
        }
            
        while (temp[len_t-1] > 10)
        {
            temp[len_t] = temp[len_t-1] / 10;
            temp[len_t-1] = temp[len_t-1] % 10;
            len_t++;
        }
        
        for (int i = 0; i < len_t; i++)
        {
            result[i] = result[i] + temp[i];
            result[i+1] = result[i+1] + result[i] / 10;
            result[i] = result[i] % 10;
        }
        
        len_r = len_t;
        while (result[len_r] > 0)
        {
            result[len_r+1] = result[len_r] / 10;
            result[len_r] = result[len_r] % 10;
            len_r++;
        }
        
    }
    
    int k = len_r - 1;
    while (result[k] == 0 && k > 0) k--;
    for (; k >= 0; k--) cout << result[k];
    cout << endl << endl << "Total Digits: " << len_r << endl;
    return 0;
}