支持負數的高精度小數加減法 C++代碼

以下支持负数的高精度小数加减法C++代码：

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

string add(string a, string b) {
    string ans = "";
    int carry = 0;
    while (a.length() < b.length()) {
        a = "0" + a;
    }
    while (a.length() > b.length()) {
        b = "0" + b;
    }
    for (int i = a.length() - 1; i >= 0; i--) {
        int sum = (a[i] - '0') + (b[i] - '0') + carry;
        ans = char(sum % 10 + '0') + ans;
        carry = sum / 10;
    }
    if (carry != 0) {
        ans = char(carry + '0') + ans;
    }
    while (ans[0] == '0' && ans.length() > 1) {
        ans.erase(0, 1);
    }
    return ans;
}

string subtract(string a, string b) {
    if (a == b) {
        return "0";
    }
    string ans = "";
    bool negative = false;
    if (a.length() < b.length() || (a.length() == b.length() && a < b)) {
        swap(a, b);
        negative = true;
    }
    while (a.length() < b.length()) {
        a = "0" + a;
    }
    while (a.length() > b.length()) {
        b = "0" + b;
    }
    for (int i = a.length() - 1; i >= 0; i--) {
        int diff = (a[i] - '0') - (b[i] - '0');
        if (diff < 0) {
            diff += 10;
            a[i - 1]--;
        }
        ans = char(diff + '0') + ans;
    }
    while (ans[0] == '0' && ans.length() > 1) {
        ans.erase(0, 1);
    }
    if (negative) {
        ans = "-" + ans;
    }
    return ans;
}

int main() {
    string a, b;
    cin >> a >> b;
    string sum = add(a, b);
    cout << "The sum of " << a << " and " << b << " is " << sum << endl;
    string difference = subtract(a, b);
    cout << "The difference between " << a << " and " << b << " is " << difference << endl;
    return 0;
}

该代码使用字符串表示高精度小数，其中负数表示为在最前面添加负号。add函数实现了两个高精度小数的加法，subtract函数实现了两个高精度小数的减法。在subtract函数中，如果a小于b，则先交换a和b，然后在答案前添加负号以表示结果为负数。