坐标运动 C++ 正则表达式

#include <iostream>
#include <string>
#include <regex>
#include <map>

using namespace std;

int main(int argc, char *argv[])
{
    string str, temp, pattern = "[ADWS]\\d{1,2}$";
    regex r(pattern);

    pair<int, int> p = {0, 0};
    while(getline(cin, str, ';'))
    {
        if(!regex_match(str, r)) continue;
        switch(str[0])
        {
            case 'A':
                {
                    p.first -= stoi(string(str.begin() + 1, str.end()));
                    break;
                }
            case 'D':
                {
                    p.first += stoi(string(str.begin() + 1, str.end()));
                    break;
                }
            case 'W':
                {
                    p.second += stoi(string(str.begin() + 1, str.end()));
                    break;
                }
            case 'S':
                {
                    p.second -= stoi(string(str.begin() + 1, str.end()));
                    break;
                }
        }
    }
    cout << p.first << "," << p.second << endl;
    return 0;
}