Thread: Help me understand this program

Hi all,

My teacher used the following example to teach us about multiple-dimension arrays:

Code:

/* Deals a random hand of cards */

#include <stdbool.h>   /* C99 only */
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define NUM_SUITS 4
#define NUM_RANKS 13

int main(void)
{
  bool in_hand[NUM_SUITS][NUM_RANKS] = {false};
  int num_cards, rank, suit;
  const char rank_code[] = {'2','3','4','5','6','7','8',
                            '9','t','j','q','k','a'};
  const char suit_code[] = {'c','d','h','s'};

  srand((unsigned) time(NULL));

  printf("Enter number of cards in hand: ");
  scanf("%d", &num_cards);

  printf("Your hand:");
  while (num_cards > 0) {
    suit = rand() % NUM_SUITS;     /* picks a random suit */
    rank = rand() % NUM_RANKS;     /* picks a random rank */
    if (!in_hand[suit][rank]) {
      in_hand[suit][rank] = true;
      num_cards--;
      printf(" %c%c", rank_code[rank], suit_code[suit]);
    }
  }
  printf("\n");

  return 0;
}

The part that I don't understand is this:

Code:

suit = rand() % NUM_SUITS;
rank = rand() % NUM_RANKS;

There are 4 suits, ranging from 0 to 3, and 13 ranks, ranging from 0 to 12. The value returned by the statements above can only return 0 to 9; doesn't that mean it's going to leave out some ranks, and possibility going out of bound for suits?

Obviously I'm new to C (and programming in general), and I've only gotten to arrays, so please take that into consideration when you explain things.

Much thanks!

claudiu,

Lol, I see how it works now. I was thinking about a large number generated by rand() divided by a variable.
Wow, I feel so stupid now...