CODEWITHSUNDEEP
c++randomblackjack
Michael Ramos
Michael Ramos

Reputation: 39

C++ generating rand numbers

In C++ is it possible to use rand to generate a number between 1-52, but stating that it cant be 23? Like for instance creating a blackjack game, you would need to make sure a player cant get the same card after randomly generating the first.

Upvotes: 2

Views: 2269

Answers (6)

Pete Becker
Pete Becker

Reputation: 76285

Sure.

int i = 23;
while (i == 23)
    i = rand() % 52 + 1;

It's quite common to discard unacceptable values when generating random numbers with a required distribution.

For a blackjack game, though, you need to deal more than one card. It's better to have a full deck and shuffle it (std::random_shuffle), then take cards from one end of whatever container holds the deck.

Upvotes: 13

user823738
user823738

Reputation: 17521

Another cool way to do this is with an array.

Create a vector:

std::vector<int> possibilities;

Insert possible values to it:

possibilities.push_back(0);
possibilities.push_back(1);
possibilities.push_back(10);

And then pick a random one from it:

int random = possibilites[ rand() % possibilites.size() ];

Upvotes: 0

Prashant Kumar
Prashant Kumar

Reputation: 22529

Here's a program that makes a deck from 1 to 52 (inclusive) and prints the deck. This features STL (and a slightly dated C++ accent)

#include <algorithm>    // std::random_shuffle
#include <ctime>        // std::time
#include <cstdlib>      // std::rand, std::srand
#include <iostream>     // std::cout
#include <vector>       // std::vector

int main() {
    std::vector<int> deck;

    // Create deck; deck creation logic goes inside loop
    for (int i = 1; i <= 52; ++i) {
        deck.push_back(i);
    }

    // initialize random number generator and shuffle deck
    std::srand(std::time(0));
    std::random_shuffle(deck.begin(), deck.end());

    // print entire deck
    while (!deck.empty()) {
        int card = deck.back();    // draw card
        std::cout << "Drew " << card << '\n';
        deck.pop_back();           // remove card from deck
    }
}

Upvotes: 1

Mike Seymour
Mike Seymour

Reputation: 254461

int value = rand(1,51);
if (value >= 23) ++value;

where rand(a,b) gives a number in the range [a,b], and could be implemented as std::rand() % (b-a+1) + a, with the caveat that that wouldn't quite be a uniform distribution.

Upvotes: 4

dlock
dlock

Reputation: 9577

int n=(rand() % 52)+ 1;
while(n==23)
n= n=(rand() % 52) + 1;

http://www.cplusplus.com/reference/cstdlib/rand/

Upvotes: 0

Happy Green Kid Naps
Happy Green Kid Naps

Reputation: 1673

Take a look at std::random_shuffle.

Upvotes: 0

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