求大佬，为什么第一个过不了啊，测试点是对的

#include<bits/stdc++.h>

using namespace std;

char a1[10001], a2[10001];
int  s1[10001], s2[10001];
long long  c[10001];

int main()
{
    scanf("%s%s", a1, a2);

    int la1 = strlen(a1);
    int la2 = strlen(a2);
    for (int i = 0; i < la1; i++)
        s1[la1 - i] = a1[i] - '0';

    for (int i = 0; i < la2; i++)
        s2[la2 - i] = a2[i] - '0';

    int lc = la1 + la2;

    for (int i = 1; i <= la1; i++)
        for (int j = 1; j <= la2; j++)
        {
            c[i + j-1] += (long long)s1[i] * s2[j];
            c[i + j ] += c[i + j-1] / 10;
            c[i + j-1] %= 10;
        }

    if (c[lc] == 0 && lc > 0)lc--;

    for (int i = lc; i > 0; i--)
        cout << c[i];

    return 0;
}