Im trying to shuffle a deck of cards but random_shuffle produces the same result every time
voidDeck::shuffle() {cout << "SHUFFLING CARDS!!!\n\n";srand(time(0));random_shuffle(cards.begin(), cards.end());displayCards();}Best Answer
That's because you seed pseudo-random number generator to the same value each time:
srand(time(0));The granularity of time are seconds, if I'm not mistaken. If you pause the execution for some time between calls to Deck::shuffle() you should see different results.
Remove that line from the function and call it once at the start of your program.
I think that the problem is because you are putting srand(...) inside of your function.
Try to move it outside (so that it will be executed only once)
You are reseeding the random number generator each time you call shuffle.
You should only seed the random number generator once per application (typically in your application initialization):
int main(){// other initializationsrand(time(NULL)); // seed the number generator// ...}It is important to know that to be able to receive a "random" number you have to seed the generator. Also it should be seeded outside the function.
srand(time(NULL));The use of the time function will help ensure that you will receive a random number.
time.h does need to be included for it to work. For more reference on srand, click here.
I'm not familiar with random_shuffle, but here's a function that does a perfect shuffle - in other words, each 52! permutations of the deck has to be equally likely.
This is from Gayle Laakmann's Cracking the Coding Interview (Question 20.2)
void Deck::shuffle() {int temp, index;for (int i = 0; i < cards.size(); i++){index = (int) (rand() %(cards.size() - i)) + i;temp = cards[i];cards[i] = cards[index];cards[index] = temp;}}