从十六进制转换为二进制C++

#include<iostream>
#include<string>
#include <bitset>

using namespace std;

string hexToBinary(string hex) {
    string binary = "";
    for (char c : hex) {
        switch (c) {
            case '0': binary += "0000"; break;
            case '1': binary += "0001"; break;
            case '2': binary += "0010"; break;
            case '3': binary += "0011"; break;
            case '4': binary += "0100"; break;
            case '5': binary += "0101"; break;
            case '6': binary += "0110"; break;
            case '7': binary += "0111"; break;
            case '8': binary += "1000"; break;
            case '9': binary += "1001"; break;
            case 'A': binary += "1010"; break;
            case 'B': binary += "1011"; break;
            case 'C': binary += "1100"; break;
            case 'D': binary += "1101"; break;
            case 'E': binary += "1110"; break;
            case 'F': binary += "1111"; break;
            default: break;
        }
    }
    return binary;
}

int main() {
    string hex;
    cout << "请输入十六进制数：";
    cin >> hex;
    string binary = hexToBinary(hex);
    cout << "转换为二进制后的结果为："<< binary<< endl;
    return 0;
}