闲来无事写了一个高精度四则运算，结果除法部分遇到了一些问题。
以下是除法部分的代码。

int compare(const std::string& lhs, const std::string& rhs) {
    if (lhs.length() < rhs.length()) return -1;
    if (lhs.length() > rhs.length()) return 1;
    for (size_t i = 0; i < lhs.length(); i++) {
        if (lhs[i] < rhs[i]) return -1;
        if (lhs[i] > rhs[i]) return 1;
        }
    }
    
    std::string divide(std::string dividend, std::string divisor) {
    if (divisor == "0") return "Error: Divisor is zero"; 
    if (compare(dividend, divisor) < 0) return "Error: Divisor is greater than dividend"; 

    std::string quotient = "";
    std::string remainder = "0";
    for (size_t i = 0; i < dividend.length(); ++i) {
    if (remainder == "0") {
        remainder = dividend[i];
    } else {
        remainder = remainder + dividend[i];
    }
    int count = 0;
    while (compare(remainder, divisor) >= 0) {
        remainder = subtract(remainder, divisor);
        ++count;
    }
    quotient += char(count + '0');
    }
    while (quotient.length() > 1 && quotient[0] == '0') quotient.erase(0, 1); 
    return quotient;
    }

其中的subtract函数代码片段在这：

std::string subtract(std::string a, std::string b) {
        std::string result;
        while (b.size() < a.size()) b = "0" + b;
        for (int i = a.size() - 1; i >= 0; --i) {
            if (a[i] < b[i]) {
                a[i] += 10;
                a[i - 1]--;
            }
            result = char(a[i] - b[i] + '0') + result;
        }
        while (result.size() > 1 && result[0] == '0') result.erase(0, 1);
        return result;
    }

目前的问题是这样的，如果输入过大数字(具体多大我懒得去试了)，程序输出1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001 反之则正常。
请问有大佬知道怎么解决吗？

Tips：程序是我经过AI的思路写的。减法函数确定没有异常，减法默认a比b大。