Any way I can make my program NOT select the same string in the array twice?

[david12345]

Hi. I am writing a program that takes 8 soccer teams and draws them randomly to play against each other. Every time the program runs, it selects the same team twice, or even more. I know what the problem is, and why that happens, but I do not know how I can fix it.

Is there any way I can fix that?
Thank you so much for any help!

Here is what I have right now...

**********************************

#include <iostream>
#include <windows.h>
#include <string>
#include <time.h>
using namespace std;

void draw();

int main()
{

char start;

cout << "\t\tWELCOME TO THE UEFA CHAMPIONS LEAGUE QUARTER FINALS DRAW " << endl;
cout << "\n\t\tTHE DRAW WILL INCLUDE THE FOLLOWING TEAMS: " << endl;
cout << "\n\t. REAL MADRID (ESP) ";
cout << "\n\t. BARCELONA (ESP) ";
cout << "\n\t. BAYERN MUNCHEN (GER) ";
cout << "\n\t. CHELSEA (ENG) ";
cout << "\n\t. PARIS SAINT GERMAIN (FRA) ";
cout << "\n\t. ARSENAL (ENG) ";
cout << "\n\t. DORTMUND (GER) ";
cout << "\n\t. JUVENTUS (ITA) ";

cout << "\n\t\tTHERE ARE NO RULES IN REGARDS TO WHICH TEAM CAN PLAY WHO. ANYONE CAN DRAW ANYONE! " << endl << endl;

cout << "\tTO START THE DRAW, PLEASE PRESS S AND ENTER! GOOD LUCK TO ALL TEAMS! ";
cin >> start;


if ((start == 's') || (start == 'S'))
{
draw();
}
else
{
cout << "\n\t\tINVALID ENTRY! THE PROGRAM WILL NOW CLOSE! OPEN AGAIN AND ONLY PRESS S TO START THE DRAW! " << endl;
Sleep(5000);
exit(0);
}


return 0;
}

void draw()
{
string teams[8] = {"REAL MADRID", "BARCELONA", "BAYERN MUNCHEN", "CHELSEA FC", "PARIS SAINT GERMAIN", "ARSENAL", "DORTMUND", "JUVENTUS"};

for (int i = 0; i < 4; i++)
{
time(NULL);
srand(time(NULL));
Sleep(2000);
cout << "\n\t" << teams[(rand() % 8)] << "\tvs. ";
Sleep(2000);
cout << "\t" << teams[(rand() % 8)] << endl;
}

}

********************************************

[48T7M4Gy]

Create a parallel array ( ie the index number of teams array and the new one correspond to each other) that stores a 0 or 1 depending upon whether it has been already selected.

If the draw() selects a team already drawn discard that selection and get another one.

[gunnerfunner]

1. Store the teams in a standard library container that supports std::random_shuffle(), instead of a C-style array
2. std::random_shuffle() the container, select the team from the front or back of the container, as per container rules
3. pop_back() or pop_front as required
4. repeat

Just make sure Arsenal get an 'easy' draw ;)

[JLBorges]

#include <iostream>
#include <string>
#include <ctime>
#include <random>
#include <algorithm>
#include <thread>
#include <chrono>

void draw( std::string teams[], std::size_t num_teams ) ;

int main()
{
    std::cout << "Welcome to the UEFA Champions League quarter finals draw\n"
              << "\nThe draw will include the following teams:\n\n" ;

    const std::size_t NTEAMS = 8 ;
    std::string teams[NTEAMS] =
    {
        "Real Madrid (ESP)",
        "Barcelona (ESP)",
        "Bayern Munchen (GER)",
        "Chelsea (ENG)",
        "Paris Saint Germain (FRA)",
        "Arsenal (ENG)",
        "Dortmund (GER)",
        "Juventus (ITA)"
    };
    
    // http://www.stroustrup.com/C++11FAQ.html#for
    for( const std::string& team_name : teams ) std::cout << '\t' << team_name << '\n' ;

    std::cout << "\nThere are no rules in regards to which team can play who.\n"
              << "Anyone can draw anyone!\n\n"
              << "To start the draw, please press s and enter!\n"
              << "Good luck to all teams!\n\n";

    char start ;
    std::cin >> start;

    if ( (start == 's') || (start == 'S') ) draw( teams, NTEAMS ) ;
    else
    {
        std::cout << "\nInvalid entry! the program will now close!\n"
                  << "Open again and only press s to start the draw!\n" ;
    }
}

void draw( std::string teams[], std::size_t num_teams )
{
    // random number engine, seeded with the current time
    // http://en.cppreference.com/w/cpp/numeric/random
    std::mt19937 rng( std::time(nullptr) ) ;

    // shuffle the teams in the array like we would shuffle a pack of cards
    // http://en.cppreference.com/w/cpp/algorithm/random_shuffle
    // note that std::random_shuffle is deprecated in C++14 and is removed in C++17
    std::shuffle( teams, teams+num_teams, rng ) ; // use std::shuffle in new code

    // print out the pairings
    for( std::size_t i = 0 ; i < num_teams ; i += 2 )
    {
        // http://en.cppreference.com/w/cpp/thread/sleep_for
        std::this_thread::sleep_for( std::chrono::seconds(1) ) ;
        std::cout << "\n\t" << teams[i] << " vs. " << teams[i+1] << '\n' ;
    }

    // if the number of teams is odd, there would be one unpaired team
    // (the function draw() is generic; we need not hard code for eight teams
    if( num_teams%2 == 1 ) std::cout << "\n\t" << teams[num_teams-1] << " gets a bye\n" ;
}

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