C++ 大数阶乘求取--数组实现代码

1. 大数阶乘理论

2. 大数阶乘实现

​​http://hi.baidu.com/urzalknsyzchrur/item/3934e84e821b7de31381da8d​​

#include <iostream>
#include <cstdlib>
#include <string>
#include <stdio.h>

using namespace std;

int main(int argc, char *argv[])
{
  int n = 0;
  cout << "Please input the number for Factorial operate : ";
  cin  >> n;

  int LargeNumberFactorial[10000] = {0};
  LargeNumberFactorial[0]    = 1;        // 0! = 1 
  LargeNumberFactorial[1]    = 1;        // 第一位对应的数值初始为 1    
  int          digit         = 1;        // n!阶乘求取的位数初始为 1 

  for (int i = 1; i <= n; i++)           // 1,2,3,...,n
  {
    for (int j = 1; j <= digit; j++)
    {
      LargeNumberFactorial[j] *= i;  
    }
    
    for (int j = 1; j <= digit; j++)
    {
      if (LargeNumberFactorial[j] > 10)
      {
        for (int r = 1; r <= digit; r++)
        {
          if (LargeNumberFactorial[digit] > 9)
          {
            digit++;
          }
          LargeNumberFactorial[r+1] += LargeNumberFactorial[r]/10;
          LargeNumberFactorial[r]   %= 10;
        }
      }
    }
  }

  cout << n << "!= ";
  for (int k = digit; k > 0; k--)
  {
    cout << LargeNumberFactorial[k];
  }
  cout << endl;

  return 0;
}