阶乘统计0个数 算法

#include<stdio.h>
#include<stdlib.h>
#include<string.h>


void calculate(int a[] , const int num );  //计算每一步的阶乘

int len = 1;

int main(void)
{

   int *a;

   int n  = 0;
   
   while(n>10000 ||n < 1000)
   {
	 printf("please input number n between 1000 and 10000: ");
     scanf("%d",&n);
   }
   
   a = (int *)malloc(sizeof(int)*n*4);
   if(a == NULL)
   {
     exit(-1);
   }
   
   memset(a,0,n);
   a[0] = 1 ;

   for(int i = 1 ; i <= n ; i++)  //通过数组计算n！
   {  
       calculate(a , i ) ;
   }
   
   
    int count = 0;
    while(a[count] == 0)
	{
	    count++;
	}//统计个数零

	printf("the result is :  %d\n",count);

   
   return 0;
}


void calculate(int a[]  , const int num )
{
   
   int result = 0;       // 乘积结果
   int remainder = 0 ;   // 余数
   int carry = 0;        // 进位

   for(int i = 0 ; i < len ; ++i)
   {
      
	   result =  a[i]*num + carry;
	   
	   a[i] = result%10;
	   carry = result/10;
   }


   if(carry!=0)  //如果进位不为零，从低位到高位依次存储
   {
       while(carry/10 != 0)
	   {
	       a[len] = carry%10;
		   carry = carry/10;
		   len++;
	   }

       a[len++] = carry;

   }
}