Create function that returns random numbers in C

Question

I need to create a function that returns random numbers without repetition between 2 intervals.

I wanted to create a kind of a card game, where the cards are shuffled, and when they return they never come out again.

In my code is repeating the values.

^{Code removed for privacy reasons}

Answer 1

Random function

I imagine you just want to use a function like this. Creating one is not a very simple task. better use what is already ready.

#include <time.h>
#include <stdlib.h>
#include <stdio.h>

int main(void) {
    srand(time(NULL));
    int r = rand() %13; //é número de cartas de cada naipe
    printf("Número sorteado %d", r);
    return 0;
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.

Documentation of the function rand() and srand() can be found here.

Algorithm without repetition

I believe the complete solution you are accurate is based on the algorithm Fisher-Yates. Something like that (if I agree with that response in the OS):

int rand_int(int n) {
    int limit = RAND_MAX - RAND_MAX % n;
    int rnd;

    do {
        rnd = rand();
    } while (rnd >= limit);
    return rnd % n;
}

void shuffle(int *array, int n) {
    int i, j, tmp;

    for (i = n - 1; i > 0; i--) {
        j = rand_int(i + 1);
        tmp = array[j];
        array[j] = array[i];
        array[i] = tmp;
    }
}

So now is to adapt to your need.

Deck

I found an example more or less ready for what you want on that page.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define CARDS 52
#define DRAW 5

void showcard(int card);

int main() {
    int deck[CARDS];
    int c;

/* initialize the deck */
    for (int x = 0; x < CARDS; x++) deck[x] = 0;
    srand((unsigned)time(NULL));
    for (int x = 0; x < DRAW; x++) {
        for(;;) {                 /* loop until a valid card is drawn */
            c = rand() % CARDS;     /* generate random drawn */
            if(deck[c] == 0) {       /* has card been drawn? */
                deck[c] = 1;        /* show that card is drawn */
                showcard(c);        /* display card */
                break;              /* end the loop */
            }
        }                       /* repeat loop until valid card found */
    }
}

void showcard(int card) {
    char *suit[4] = { "Spades", "Hearts", "Clubs", "Diamonds" };
    switch (card % 13) {
        case 0:
            printf("%2s","A");
            break;
        case 10:
            printf("%2s","J");
            break;
        case 11:
            printf("%2s","Q");
            break;
        case 12:
            printf("%2s","K");
            break;
        default:
            printf("%2d",card%13+1);
    }
    printf(" of %s\n",suit[card/13]);
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.