51nod 1057 N的阶乘

#include<iostream>
#include<cstdio>
using namespace std;
const int MAXN=40000;
int a[MAXN]={1,1};
int main()
{
int c=1,n,j;
int carry;
scanf("%d",&n);
for(int i=2;i<=n;i++)
{
for(j=1,carry=0;j<=c;j++)
{
int r=a[j]*i+carry;
a[j]=r%10000;
carry=r/10000;
}
while(carry)
{
a[++c]=carry%10000;
carry/=10000;
}
}
printf("%d",a[c]);
for(int i=c-1;i>=1;i--)
printf("%04d",a[i]);
printf("\n");
return 0;
}