Найдите ошибку в коде С++

#include<cstdio>
const int l = 1001;
int a[l][l];
char s1[l], s2[l], p[l];
int max (int i, int j)
{
   if (i > j)
   return i;
   else
   return j;
}
 
int len_str(int n)
{
   for (int i = n; i >= 0; i--)
    for (int j = n; j >= 0; j--)
   {
    if ((s1[i] == '\0') || (s2[j] == '\0'))
     a[i][j] = 0;
    else
     {
      if (s1[i] == s2[j])
       a[i][j] = a[i+1][j+1] + 1;
      else
        a[i][j] = max (a[i+1][j], a[i][j+1]);
     }
   }
return a[0][0];
}
 
void s_pal(int n)
{
int i = 0, j = 0, k = 0;
while (k < n)
{
if (a[i][j+1] == a[i][j])
j++;
else
{
if (a[i+1][j] == a[i][j])
i++;
else
{
p[k] = s1[i];
k++;
i++;
j++;
}
}
}
 
}
 
int main()
{
int n, lp;
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
n = 0;
while (!feof(stdin))
{
s1[n] = getchar();
n++;
}
s1[n-1] = '\0';
for (int i = 0; i < n; i++)
s2[n-i-2] = s1[i];
s2[n-1] = s1[n-1];
lp = len_str(n);
for (int i = 0; i < n; i++)
s_pal(lp);
printf("%d\n", lp);
printf("%s", p);
return 0;
}