求助啊，五个点，四个过，一个直接re，不懂啊

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;int as[1005], bs[1005], c[2005];int main  () {  string a, b;
    cin >> a >> b;reverse(a.begin(), a.end());reverse(b.begin(), b.end());int la = a.size();int lb = b.size();
    for (int i = 0; i < la; i++) {
        as[i] = a[i] - 48;
    }
    for (int i = 0; i < lb; i++) {
        bs[i] = b[i] - 48;
    }
    for (int i = 0; i <= la; i++) {
        for (int j = 0; j <= lb; j++) {
            c[i + j] = c[i + j] + as[i] * bs[j];
        }
    }
    for (int i = 0; i <= 2000; i++) {
        if (c[i] > 9) {
            c[i + 1] += c[i] / 10;
            c[i] %= 10;
        }
    }
    int i = 2000;
    while (c[i] == 0 && i != 0) {
        i--;
    }
    for (int j = i; j >= 0; j--) {
        cout << c[j];
    }
    return 0;
}