Shuffle

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define N 10

unsigned char **make(int n) {
  unsigned char **p = (unsigned char **) malloc(N * sizeof(unsigned char *));
  for (int i = 0; i < n; i++) {
    p[i] = (unsigned char *) malloc(BUFSIZ);
    sprintf((char *) p[i], "Q%d.", i);
  }
  return p;
}

void print_problem(unsigned char **problem, int n) {
  for (int i = 0; i < N; i++) {
    printf("%s ", problem[i]);
  }
  printf("\n");
}

void shuffle(unsigned char **problem, int n) {
  srand((unsigned int) time(NULL));
  for (int i = n - 1; i > 0; i--) {
    int j = rand() % (i + 1);
    unsigned char *swap = problem[i];
    problem[i] = problem[j];
    problem[j] = swap;
  }
}

int main(int argc, char **argv) {
  unsigned char **problem = make(N);
  printf("Before:\n");
  print_problem(problem, N);
  shuffle(problem, N);
  printf("After:\n");
  print_problem(problem, N);
  return EXIT_SUCCESS;
}