1172：求10000以内n的阶乘

#include<iostream>
#include<cstring>
#define N 100010
using namespace std;
int n,a[N],lena=1;
int main(){
    cin>>n;
    if(n==0){
        cout<<0<<endl;
        return 0;
    }
    a[0]=1;
    for(int k=2;k<=n;k++){
        for(int i=0;i<lena;i++)a[i]*=k;
        for(int i=0;i<lena;i++){
            if(a[i]>9){
                a[i+1]+=a[i]/10;
                a[i]%=10;
                if(i==lena-1)lena++;
            }
        }
    }
    for(int i=lena-1;i>=0;i--)cout<<a[i];
    cout<<endl;
}