can anyone tell me whats wrong with my code. it displays wrong answer test #15

#include<iostream>
#include<string.h>
using namespace std;
int main()
{
    long int n;
    long int ans=1;
    char k[20];
    cin>>n>>k;
    if(n<1||n>10)
                 return 0;
    long int res;
    res=n%strlen(k);
    long int i=0,length=strlen(k);
    if(length<1||length>20)
           return 0;

    if(res==0)
    {
        while(n-i*length>=length)
        {
                       ans=ans*(n-i*length);
                       i++;
        }
    }
    else
    {
        while(n>=i*length)
        {
                       ans=ans*(n-i*length);
                       i++;
        }
    }
    cout<<ans;
    return 0;
}

Edited by author 21.08.2010 11:32

15 test
n=10
k=20

it's last test

> char k[20]
You forgot about the null character ( '\0' ). Correct is
char k[21]