请问为什么这个高精度类在运算时死循环/RE了？

class int_t
{
private:
    int len,a[45];
public:
    int_t(int q=0)
    {
        if(q)while(a[++len]=q%10,q/=10);
    }
    int&operator[](int x)
    {
        return a[x];
    }
    friend std::ostream&operator<<(std::ostream&a,int_t n)
    {
        for(int i=n.len;i;--i)putchar(n[i]^48);
        return a;
    }
    friend int_t&operator+=(int_t&a,int_t b)
    {
        if(b.len>a.len)a.len=b.len;
        int i;
        for(i=1;i<=a.len;++i)a[i]+=b[i];
        for(i=1;i<=a.len;++i)a[i+1]+=a[i]/10,a[i]%=10;
        if(a[a.len+1])++a.len;
        return a;
    }
    int_t count()
    {
        int i;
        for(i=1;i<=len;++i)a[i]<<=1;
        for(i=1;i<=len;++i)a[i+1]+=a[i]/10,a[i]%=10;
        if(a[len+1])++len;
        return *this;
    }
}ans;