哪错了

#include<stdio.h>
#include<cstdlib>
#include<string.h>
#include<math.h>
#define maxn 570
typedef struct
{
    long a[maxn];
}bign;
void mul(bign &c,bign &a,bign &b)
{
    memset(c.a,0,sizeof(c.a));
    for(long i=0;i<=499;i++)
      for(long j=0;j<=499-i;j++)
        c.a[i+j]+=a.a[i]*b.a[j];
    for(long i=0;i<=499;i++)
      if(c.a[i]>=10)
      {
         c.a[i+1]+=c.a[i]/10;
         c.a[i]%=10;
      }
    c.a[500]=0;
}
int main()
{
    long n,m,count;
    bign _2[maxn]={{1},{2}},ans={{1}},t;
    scanf("%ld",&n);
    //  Input
    printf("%ld\n",(long)(n*log10(2))+1);
    m=(long)(log(n)/log(2))+3;
    for(long i=2;i<=m;i++)
      mul(_2[i],_2[i-1],_2[i-1]);
    count=0;
    while(n>0)
    {
       if(n%2==1)
       {
          t=ans;
          mul(ans,t,_2[count+1]);
       }
       count++;n/=2;
    }
    ans.a[0]--;
    for(long i=499;i>=0;i--)
      printf("%ld",ans.a[i]);
    putchar('\n');
system("pause");
}