abort()

    for (int i = 0; i < countClients; i++) {
        system("START C:\\Users\\User\\Documents\\projects\\WinSock\\Debug\\Client.exe");
        newConnection = accept(sListen, (SOCKADDR*)&addr, &sizeofaddr);
        if (newConnection == 0) {
            cout << "Error connecting\n";
        }
        cout << "Client connected\n";
        CreateThread(NULL, 0, func, (LPVOID)newConnection, 0, &thread);
    }

#include "stdafx.h"
#include <WinSock2.h>
#include <iostream>
#include <string>
#include <vector>
#include <Windows.h>
using namespace std;
 
#pragma comment(lib, "ws2_32.lib")
#pragma warning(disable: 4996)
 
//vector <SOCKET> Connections;
//vector <HANDLE> Threads;
//int nclients = 0;
//int nthreads = 0;
 
string letters_russia = "йцукенгшщзхъфывапролджэячсмитьбюЙЦУКЕНГШЩЗХЪФЫВАПРОЛДЖЭЯЧСМИТЬБЮ";
 
DWORD WINAPI func(LPVOID tmp) {
    cout << "Thread is created\n" << endl;
 
    SOCKET current_client = (SOCKET)tmp;
    int msg_to_client_size;
    int msg_from_client_size;
    string msg_to_client;
    string in_password = "Input the password: ";
    string good_password = "Password is correct";
    int in_password_size = in_password.size();
    int good_password_size = good_password.size();
 
    while (true) {
        bool is_digit = true;
        send(current_client, (char*)&in_password_size, sizeof(int), NULL);
        send(current_client, in_password.c_str(), in_password_size, NULL);
 
        recv(current_client, (char*)&msg_from_client_size, sizeof(int), NULL);
        char *msg_from_client = new char[msg_from_client_size + 1];
        msg_from_client[msg_from_client_size] = '\0';
        recv(current_client, msg_from_client, msg_from_client_size, NULL);
 
        for (int i = 0; i < msg_from_client_size; i++) {
            if ((msg_from_client[i] >= 'a' && msg_from_client[i] <= 'z')
                || (msg_from_client[i] >= 'A' && msg_from_client[i] <= 'Z') || msg_from_client[i] == letters_russia[i]) {
                is_digit = false;
                break;
            }
        }
 
        if (msg_from_client_size > 4 || is_digit == false) {
            cout << "Incorrect password, repeat input after 40 seconds" << endl;
            Sleep(40000);
        }
        else {
            send(current_client, (char*)&good_password_size, sizeof(int), NULL);
            send(current_client, good_password.c_str(), good_password_size, NULL);
            break;
        }
    }
 
    while(true) {
        recv(current_client, (char*)&msg_from_client_size, sizeof(int), NULL);
        char *msg_from_client = new char[msg_from_client_size + 1];
        msg_from_client[msg_from_client_size] = '\0';
        recv(current_client, msg_from_client, msg_from_client_size, NULL);
 
        if (strcmp(msg_from_client, ".") == 0) {
            msg_to_client = ".";
            msg_to_client_size = msg_to_client.size();
            send(current_client, (char*)&msg_to_client_size, sizeof(int), NULL());
            send(current_client, msg_to_client.c_str(), msg_to_client_size, NULL);
            closesocket(current_client);
            ExitThread(0);
        }
        cout << msg_from_client << endl;
        send(current_client, (char*)&msg_from_client_size, sizeof(int), NULL());
        send(current_client, msg_from_client, msg_from_client_size, NULL);
 
        delete[] msg_from_client;
    }
}
 
int main() {
    setlocale(0, "RUS");
 
    int countClients;
    cout << "Input the number of clients, you want to connect: " << endl;
    cin >> countClients;
 
    WSAData wsaData;
    WORD DLLVersion = MAKEWORD(2,1); // версия библиотеки 
 
    if(WSAStartup(DLLVersion, &wsaData) != 0) {
        cout << "Error download library, code " << WSAGetLastError() << endl;
        return 1;
    }
 
    SOCKADDR_IN addr; // хранение адреса
    int sizeofaddr = sizeof(addr);
    addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    addr.sin_port = htons(1111);
    addr.sin_family = AF_INET;
 
    SOCKET sListen;
    sListen = socket(AF_INET, SOCK_STREAM, NULL);
    bind(sListen, (SOCKADDR*)&addr, sizeof(addr));
    listen(sListen, countClients);
    
    SOCKET newConnection; //сокет для соединения с клиентом
    DWORD thread;
 
    for (int i = 0; i < countClients; i++) {
        system("START C:\\Users\\User\\Documents\\projects\\WinSock\\Debug\\Client.exe");
        newConnection = accept(sListen, (SOCKADDR*)&addr, &sizeofaddr);
        if (newConnection == 0) {
            cout << "Error connecting\n";
        }
        cout << "Client connected\n";
        CreateThread(NULL, 0, func, (LPVOID)newConnection, 0, &thread);
    }
 
 
    closesocket(newConnection);
    WSACleanup();
    return 0;
}

    std::vector<HANDLE> threads;
    for (int i = 0; i < countClients; i++) {
        system("START C:\\Users\\User\\Documents\\projects\\WinSock\\Debug\\Client.exe");
        newConnection = accept(sListen, (SOCKADDR*)&addr, &sizeofaddr);
        if (newConnection == 0) {
            cout << "Error connecting\n";
        }
        cout << "Client connected\n";
 
        DWORD thread;
        HANDLE hThread = CreateThread(NULL, 0, func, (LPVOID)newConnection, 0, &thread);
        threads.emplace_back(hThread);
    }
 
 
    ::WaitForMultipleObjects(threads.size(), threads.data(), TRUE, INFINITE);
    closesocket(newConnection);
    WSACleanup();
    return 0;