#include<iostream>
#include<regex>
#include<stdio.h>
using namespace std;

bool VerifyEmail(string email)
{
     //here \w assumed as "word character", usually [A-Za-z0-9_].
 		const regex patterntypes("(\\w+)(\\.|_)?(\\w*)@(\\w+)(\\.(\\w+))+");
    return regex_match(email,patterntypes);
}
int main()
{
    string strg;
    cout<<"Enter your EmailAddrs:"<<endl;
    cin>>strg;
    if(VerifyEmail(strg))
        cout<<"Your EmailAddrs is valid"<<endl;
    else
        cout<<"Your EmailAddrs is invalid"<<endl;
    return 0;
}

#include <iostream>
#include <regex>

bool isValid(const std::string& email)
{   // regular expression
    const std::regex pattern("(\\w+)(\\.|_)?(\\w*)@(\\w+)(\\.(\\w+))+");
    return regex_match(email, pattern);
}

int main()
{
    std::cout << "enter a mail address :" << std::endl;
    std::string email;

    do {
        std::cin >> email;

        std::transform(email.begin(), email.end(), email.begin(),
            [](unsigned char c) { return std::tolower(c); });
        
        isValid(email) ? std::cout << email << " : " << "valid email" << std::endl
                       : std::cout << email << " : " << "invalid email" << std::endl;
    } while (email != "exit");
}

#include <string>
#include <cctype>
#include <iostream>
#include <algorithm>

//Util fn
char lowercase(unsigned char ch){

   if (std::isupper(ch)) 
      return std::tolower(ch);
   else if (std::islower(ch)) 
      return std::toupper(ch);
   else
      return ch;
}

int main(){
  std::string str = "jUmpjumP007";
  std::string output;
  output.resize(str.length());
  
  std::transform(str.begin(), str.end(), output.begin(), lowercase);
  std::cout << output; 
}

#include <string>
#include <ranges>
#include <iostream>
#include <cctype>
#include <string_view>
#include <vector>

namespace rngs = std::ranges;

std::vector<std::string> split(const std::string& line, char del) {
	std::vector<std::string> s;

	for (const auto& word : rngs::split_view(line, del)) {
		std::string_view n { word.begin(), word.end() };

		while (n.starts_with(' '))
			n.remove_prefix(1);

		while (n.ends_with(' '))
			n.remove_suffix(1);

		if (!n.empty())
			s.emplace_back(n.begin(), n.end());
	}

	return s;
}

std::string tolower(std::string s) {
	for (auto& ch : s)
		ch = static_cast<char>(std::tolower(static_cast<unsigned char>(ch)));

	return s;
}

std::string solve(const std::string& names, const std::string& email) {
	const auto lcemail { tolower(email) };
	const auto vn { split(names, ';')};

	std::string emails;

	for (const auto& n : vn) {
		const auto na { split(n, ' ') };

		if (!emails.empty())
			emails += "; ";

		emails += na.front() + ' ' + na.back() + " <" + tolower(na.front()) + '.' + tolower(na.back()) + '@' + lcemail + ".com>";
	}

	return emails;
}

int main() {
	std::cout << solve("  Clark Kent; Lois Lane ; ", "Example") << '\n';
	std::cout << solve("Clark Kent; Lois Lane", "DailyPlanet") << '\n';
}

#include <regex>
#include <iostream>

std::string toLower(std::string s)
{
    for (auto& c : s)
        c = tolower(c);

    return s;
}

void solve(std::string s, std::string e)
{
    std::regex regx("[\\; ]");
    std::sregex_token_iterator first{ s.begin(), s.end(), regx, -1 }, last;
    std::vector<std::string> data{ first, last };

    for (int i = 0; i < data.size() - 1; ++i)
    {
        if (i % 2) continue; // little trick
        std::cout << data[i] << " " << data[i + 1] << "\t";
        std::cout << "<" << toLower(data[i]) << "." << toLower(data[i + 1]) << "@" << e << ">" << std::endl;
    }
}

int main() 
{
    std::string input = "Clark Kent;Lois Lane;Lex Luthor";
    solve(input, "dailyplanet.com");
}