C Exercises: Shuffle the elements of an array

C Callback function: Exercise-9 with Solution

Write a C program to shuffle the elements of an array using a callback function to generate random numbers for swapping.

Sample Solution:

C Code:

#include <stdio.h>

#include <stdlib.h>

#include <time.h>

void shuffle(int * array, size_t n, int( * rand_func)(void)) {
  for (int i = n - 1; i > 0; i--) {
    int j = rand_func() % (i + 1);
    int tmp = array[i];
    array[i] = array[j];
    array[j] = tmp;
  }
}

int main() {
  int arr[] = {
    1,
    2,
    3,
    4,
    5
  };
  size_t n = sizeof(arr) / sizeof(int);
  printf("Original array elements: ");
  for (size_t i = 0; i < n; i++) {
    printf("%d ", arr[i]);
  }

  // Seed the random number generator
  srand(time(NULL));

  // Shuffle the array using rand() as the random number generator
  shuffle(arr, n, rand);

  // Print the shuffled array
  printf("\nShuffled array elements: ");
  for (int i = 0; i < n; i++) {
    printf("%d ", arr[i]);
  }
  printf("\n");
  return 0;
}

Sample Output:

Original array elements: 1 2 3 4 5 
Shuffled array elements: 3 5 2 1 4 

Note: The results may vary due to srand() function is used to seed the random number.

Explanation:

In the above program, the shuffle() function takes three arguments an array of integers, the number of elements in the array, and a callback function that generates a random integer. It then shuffles the elements of the array by iterating over the array backwards and swapping each element with a randomly chosen element from the range 0 to the current index.

In the main() function, an array of integers is created and its elements are shuffled using the shuffle() function. The rand() function is used as the callback function for generating random numbers.

Flowchart:

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