How to shuffle an array using the Fisher-Yates shuffle (also known as the Knuth shuffle: The Art of Computer Programming volume 2: Seminumerical algorithms, Algorithm P).

gistfile1.cpp

#include <algorithm>
#include <cstdlib>
#include <iterator>
#include <iostream>

#ifndef N
#define N 100
#endif

inline int rand_range(int min, int max) {
    return min + rand() / (RAND_MAX / (max - min + 1) + 1);
}

int main() {
  int data[N];
  srand(time(0));

  for (int i = 0; i < N; i++) {
    data[i] = i;
  }
  std::cout << "Data before the shuffle" << std::endl;
  std::copy(data, data+N, std::ostream_iterator<int>(std::cout,", "));
  std::cout << std::endl;


  // Shuffle the data array according to the Fisher-Yates shuffle
  for (int i = (N - 1); i > 0; --i) {
    int j = rand_range(0, i);
    int temp;
    temp = data[j];
    data[j] = data[i];
    data[i] = temp;
  }

  std::cout << std::endl << "Data after the shuffle" << std::endl;
  std::copy(data, data+N, std::ostream_iterator<int>(std::cout,", "));
  std::cout << std::endl;
  return 0;
}