Exer17_22.cpp

#include <iostream>
#include <string>
#include <regex>
using std::cout;
using std::cin;
using std::endl;
using std::string;
using std::regex;
using std::smatch;
bool valid(const string& s)
{
    string phone = "(\\()?(\\d{3})(\\))?(-|.| +)?(\\d{3})(-|.| +)?(\\d{4})";
    string space = " +";
    regex r(phone);
    regex rs(space);
    smatch m;
    if(regex_match(s, m, r))
    {
        // if there is an open parenthesis before the area code
        if(m[1].matched)
            // the area code must be followed by a close parenthesis
            // and followed immediately by the rest of the number or a space
            return m[3].matched &&
                   (m[4].matched == 0 || regex_match(m[4].str(), rs));
        else
            // then there can't be a close after the aera code
            // the delimiters between the other two components must match
            return !m[3].matched &&
                   regex_match(m[4].str(), rs) &&
                   regex_match(m[6].str(), rs);
    }
    else
        return false;
}
int main()
{
    string s;
    while(getline(cin, s))
    {
        if(valid(s))
            cout << "valid: " << s << endl;
        else
            cout << "invalid: " << s << endl;
    }
    return 0;
}