只用STRING類實現支持任意數的高精度運算

好的，以下是一个使用STRING类实现高精度运算的示例代码，支持任意数的加法、减法和乘法运算：

#include <iostream>
#include <string>

using namespace std;

string add(string num1, string num2) {
    int carry = 0;
    string result = "";
    while (num1.length() < num2.length()) {
        num1 = "0" + num1;
    }
    while (num2.length() < num1.length()) {
        num2 = "0" + num2;
    }
    for (int i = num1.length() - 1; i >= 0; i--) {
        int sum = (num1[i] - '0') + (num2[i] - '0') + carry;
        carry = sum / 10;
        result = to_string(sum % 10) + result;
    }
    if (carry > 0) {
        result = to_string(carry) + result;
    }
    return result;
}

string subtract(string num1, string num2) {
    int borrow = 0;
    string result = "";
    while (num1.length() < num2.length()) {
        num1 = "0" + num1;
    }
    while (num2.length() < num1.length()) {
        num2 = "0" + num2;
    }
    for (int i = num1.length() - 1; i >= 0; i--) {
        int diff = (num1[i] - '0') - (num2[i] - '0') - borrow;
        if (diff < 0) {
            diff += 10;
            borrow = 1;
        } else {
            borrow = 0;
        }
        result = to_string(diff) + result;
    }
    while (result.length() > 1 && result[0] == '0') {
        result = result.substr(1);
    }
    return result;
}

string multiply(string num1, string num2) {
    if (num1 == "0" || num2 == "0") {
        return "0";
    }
    int len1 = num1.length(), len2 = num2.length();
    string result(len1 + len2, '0');
    for (int i = len1 - 1; i >= 0; i--) {
        int carry = 0;
        for (int j = len2 - 1; j >= 0; j--) {
            int sum = (num1[i] - '0') * (num2[j] - '0') + (result[i + j + 1] - '0') + carry;
            carry = sum / 10;
            result[i + j + 1] = to_string(sum % 10)[0];
        }
        result[i] += carry;
    }
    while (result.length() > 1 && result[0] == '0') {
        result = result.substr(1);
    }
    return result;
}

int main() {
    string num1, num2;
    cout << "Please input two numbers: " << endl;
    cin >> num1 >> num2;
    cout << "Result of addition: " << add(num1, num2) << endl;
    cout << "Result of subtraction: " << subtract(num1, num2) << endl;
    cout << "Result of multiplication: " << multiply(num1, num2) << endl;
    return 0;
}

这段代码中使用了STRING类的基本操作，实现了任意数的高精度加法、减法和乘法运算。您可以根据需要进行修改和扩展。