cards.c

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

unsigned int get_rand(int x)
{
    unsigned int i,res,mask=0;
    if (x<=0) return 0;
    for (i=0; x>=(1<<i); i++)
        mask=(mask<<1)+1;
    while ((res=rand()&mask)>x);
    return res;
}

void swap(int* a, int* b)
{
    int t=*a; *a=*b; *b=t;
}

void random_shuffle(int arr[], int n)
{
    int i;
    for (i=n-1; i>0; i--)
        swap(arr+i, arr+get_rand(n-1));
}

int main()
{
    int i, cards[13]={1,2,3,4,5,6,7,8,9,10,11,12,13};
    srand((unsigned int)time(0));
    random_shuffle(cards, 13);
    for (i=0; i<13; i++)
        printf("%d ",cards[i]);
    printf("\n");
}