count_unique.c

/*******************************************************************************
*
* Program: Count The Unique Elements In An Array
*
* Description: A program to count the number of unique elements in an array
* using C.
*
* YouTube Lesson: https://www.youtube.com/watch?v=OH2s5jBQXvM 
*
* Author: Kevin Browne @ https://portfoliocourses.com
*
*******************************************************************************/

#include <stdio.h>
#include <stdbool.h>

int count_unique(int a[], int length);

int main()
{
  // declare and initialize a test array of 13 elements in length, with 5
  // unique elements (2,5,6,9,7).  Elements like '8' are not unique because
  // a duplicate exists in the array.
  int a[] = {1,2,3,4,5,6,3,4,1,8,9,7,8};

  // call count_unique to count the unique elements in the array, store the
  // resulting return value into total_unique
  int total_unique = count_unique(a, 13);

  // Output the number of unique elements in the array
  printf("Total Unique Elements: %d\n", total_unique);

  return 0;
}

// Returns the number of unique elements in the array a with the provided length
int count_unique(int a[], int length)
{
  // Initialize the count of unique elements 0
  int count = 0;

  // Use the counter variable i to 'loop through and check' each element in the
  // array to see if it has any duplicates, by initializing i to 0 and
  // incrementing by 1 until it reaches the array length.
  for (int i = 0; i < length; i++)
  {
    // Initially we'll assume that there is no element in the array that
    // matches the element at index i by setting match_found to false
    bool match_found = false;

    // Use the counter variable j to 'loop through and check' element in the
    // array to see if it matches the element in the array at the index i
    for (int j = 0; j < length; j++)
    {
      // if the element in the array at the index i is match (i.e equals) the
      // the element in the array at the index j, and i != j (otherwise it is
      // the same element being compared which of course equals itself), then
      // we have found a match and we can set match_found to true
      if (a[i] == a[j] && i != j)
        match_found = true;
    }

    // If we have NOT found a match, then the element is unique and we increment
    // the count of unique elements.
    if (!match_found) count++;
  }

  // After checking each element to see if it unique count will be set to the
  // number of unique elements and we can return this value.
  return count;
}