21 Sticks Game

#include <iostream>
#include <string>
#include <math.h>
#include <cstdlib>
#include <bits/stdc++.h>
using namespace std;

int main()
{
    srand(time(NULL));
    int numberPlayers, turns, numberSticks, sticksLeft;
    string player1, player2, firstName, secondName;

    sticksLeft = 21;

    cout << "Hello! Welcome to 21 Sticks. The game starts with 21 sticks,\n"; // a nice menu
    cout << "and each round, the player can choose to take 1, 2 or 3 sticks.\n";
    cout << "The last player to take a stick loses. You can play with another\n";
    cout << "person or against the computer.\n\n";

    cout << "How many people will play? " << endl; //to determine if the game is versus or against the computer
    cin >> numberPlayers;

    while (numberPlayers > 2 || numberPlayers < 1){
        cout << "Please enter a valid value (1 or 2)" << endl;
        cin >> numberPlayers;
    } //Error message

    turns = rand() % 2; //random start

    if (numberPlayers == 2){ //two player game
        cout << "Insert first player's name\n";//to call the players by their names
        cin >> firstName;
        cout << "Insert second player's name\n";
        cin >> secondName;

        if (turns == 1){ //to make it easier to alternate between players
            player1 = firstName;
            player2 = secondName;
        }else{
            player1 = secondName;
            player2 = firstName;
        }

        cout << "\n" << player2 << " goes first" << endl;

        do{
            turns++;  //keeping track of whose turn it is
            turns = turns % 2;
            if (turns == 1){ //to make it easier to alternate between players
                player1 = firstName;
                player2 = secondName;
            }else{
                player1 = secondName;
                player2 = firstName;
            }

            cout << "How many sticks do you take?\n"; //asking the player for a number
            cin >> numberSticks;

            while (numberSticks < 1 || numberSticks > 3){
                cout << "Invalid number. You can only take 1, 2 or 3 sticks.\n";
                cin >> numberSticks;
            } //Error message

            while(sticksLeft - numberSticks < 0){
                cout << "Invalid number. You can't leave negative sticks." << endl;
                cin >> numberSticks;
            } //To avoid getting negative sticks

            sticksLeft = sticksLeft - numberSticks; // keeping track of the sticks left
            if(sticksLeft == 0){ //to end the game
                break;
            }

            cout << player1 << " took " << numberSticks << " sticks. There are " << sticksLeft << " left\n\n";
            cout << player2 << " goes next" << endl;

        }while (sticksLeft > 0);

        cout << "\n" << player2 << " won!" << endl; //the last player to play lost, display who won

    }else{ // player against computer
        cout << "Insert your name " << endl;
        cin >> firstName;

        if (turns == 1){ //to make it easier to alternate between player and computer
            player1 = firstName;
            player2 = "The computer";
        }else{
            player1 = "The computer";
            player2 = firstName;
        }

        cout << "\n" << player2 << " goes first" << endl;

        if(player2 == "The computer"){
            do{
                numberSticks = 1; // if the computer goes first, it takes 1

                sticksLeft = sticksLeft - numberSticks; // keeping track of the sticks left
                if(sticksLeft == 0){ //to end the game
                    cout << "You won!";
                    break;
                }

                cout << player2 << " took " << numberSticks << " stick. There are " << sticksLeft << " left\n\n";
                cout << "How many sticks do you take?\n"; //asking the player for a number
                cin >> numberSticks;

                while (numberSticks < 1 || numberSticks > 3){
                    cout << "Invalid number. You can only take 1, 2 or 3 sticks.\n";
                    cin >> numberSticks;
                } //Error message

                while(sticksLeft - numberSticks < 0){
                    cout << "Invalid number. You can't leave negative sticks." << endl;
                    cin >> numberSticks;
                } //To avoid getting negative sticks

                sticksLeft = sticksLeft - numberSticks; // keeping track of the sticks left
                if(sticksLeft == 0){ //to end the game
                    cout << "You lost!";
                    break;
                }

                cout << player1 << " took "<< numberSticks << " sticks. There are " << sticksLeft << " left\n\n";
            }while(numberSticks==3);

            if(numberSticks==1){ //if the player doesn't take 3, the computer wins
                numberSticks = 2;

                sticksLeft = sticksLeft - numberSticks; // keeping track of the sticks left
                cout << player2 << " took " << numberSticks << " stick. There are " << sticksLeft << " left\n\n";
            }else if(numberSticks==2){
                numberSticks = 1;

                sticksLeft = sticksLeft - numberSticks; // keeping track of the sticks left
                cout << player2 << " took " << numberSticks << " stick. There are " << sticksLeft << " left\n\n";
            }

            player2 = firstName;
            player1 = "The computer";
        }

        if(player2 == firstName||sticksLeft > 0){
            do{
                cout << "How many sticks do you take?\n"; //asking the player for a number
                cin >> numberSticks;

                while (numberSticks < 1 || numberSticks > 3){
                    cout << "Invalid number. You can only take 1, 2 or 3 sticks.\n";
                    cin >> numberSticks;
                } //Error message

                while(sticksLeft - numberSticks < 0){
                    cout << "Invalid number. You can't leave negative sticks." << endl;
                    cin >> numberSticks;
                } //To avoid getting negative sticks

                sticksLeft = sticksLeft - numberSticks; // keeping track of the sticks left
                if(sticksLeft == 0){ //to end the game
                    cout << "You lost!";
                    break;
                }

                cout << player2 << " took " << numberSticks << " sticks. There are " << sticksLeft << " left.\n\n";
                cout << player1 << " goes next" << endl;

                if(numberSticks == 1){ // this is the strategy to win the game
                    numberSticks = 3;
                }else if(numberSticks == 2){
                    numberSticks = 2;
                }else if(numberSticks == 3){
                    numberSticks = 1;
                }
                sticksLeft = sticksLeft - numberSticks; // keeping track of the sticks left

                cout << player1 << " took " << numberSticks << " sticks. There are " << sticksLeft << " left.\n\n";

            }while(sticksLeft > 0);
        }
    }
    return 0;
}