高精度求调，乘法错误但调不了

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 3000;
struct Bigint {
    int len, a[MAXN];//len->length, a[MAXN]->values
    Bigint(int x = 0) {
        memset(a, 0, sizeof(a));
        for (len = 0; x; len++) {
            a[len] = x % 10, x /= 10;
        }
    }
    int &operator[](int i) {
        return a[i];
    }
    void flatten(int L) {
        for (int i = 0; i < L; i++) {
            a[i + 1] += a[i] / 10, a[i] %= 10;
        }
        len = L;
        for (; !a[len];) {
            len--;
        }
    }
    void print(const char* s = "") {// s 用作调试
        for (int i = max(len - 1, 0); i >= 0; i--) {
            printf("%d%s", a[i], s);
        }
    }
};
Bigint operator*(Bigint a, int b) {
    Bigint c;
    int len = a.len;
    for (int i = 0; i < len; i++) {
        c[i] = a[i] * b;
    }
    c.flatten(len + 11);
    return c;
}
int main() {
    int t;
    cin >> t;
    while(t--) {
        int n, a;
        cin >> n >> a;
        Bigint fac = 1;
//        fac.print("==fac\n");
        for(int i = 2; i <= n; i++) {
            fac = fac * i;
        }
        int cnt = 0;
        for(int i = 0; i < fac.len; i++) {
            if(fac[i] == a) {
                cnt++;
            }
        }
        cout << cnt << endl;
    }
    return 0;
}