shuffle.c

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/*
** Use random numbers to shuffle the "cards" in the deck.  The second
** argument indicates the number of cards.  The first time this
** function is called, srand is called to initialize the random
** number generator.
*/
#include <stdlib.h>
#include <time.h>
#define	TRUE	1
#define	FALSE	0

void shuffle( int *deck, int n_cards )
{
	int	i;
	static	int	first_time = TRUE;

	/*
	** Seed the random number generator with the current time
	** of day if we haven't done so yet.
	*/
	if( first_time ){
		first_time = FALSE;
		srand( (unsigned int)time( NULL ) );
	}

	/*
	** "Shuffle" by interchanging random pairs of cards.
	*/
	for( i = n_cards - 1; i > 0; i -= 1 ){
		int	where;
		int	temp;

		where = rand() % i;
		temp = deck[ where ];
		deck[ where ] = deck[ i ];
		deck[ i ] = temp;
	}
}