如何在C++中实现十六进制到十进制的递归转换？

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

int hexToDec(string hexStr) {
    if (hexStr.empty()) {
        return 0;
    }
    
    char lastChar = hexStr.back();
    hexStr.pop_back();
    
    int lastDigit;
    if (lastChar >= '0' && lastChar <= '9') {
        lastDigit = lastChar - '0';
    } else if (lastChar >= 'A' && lastChar <= 'F') {
        lastDigit = lastChar - 'A' + 10;
    } else if (lastChar >= 'a' && lastChar <= 'f') {
        lastDigit = lastChar - 'a' + 10;
    } else {
        // 非法字符处理，这里可以根据实际需求进行修改
        return hexToDec(hexStr);
    }
    
    return hexToDec(hexStr) * 16 + lastDigit;
}

int main() {
    string hexStr = "1A";
    int decNum = hexToDec(hexStr);
    cout << "Hexadecimal: " << hexStr << endl;
    cout << "Decimal: " << decNum << endl;
    
    return 0;
}