C Program Count the Number of Occurrences of an Element an array using Recursion

C Program Count the Number of Occurrences of an Element an array using Recursion - Source code

void occur(int [], int, int, int, int *);
 
int main()
{
    int size, key, count = 0;
    int list[40];
    int i;
 
    printf("Enter the size of the list: ");
    scanf("%d", &size);
    printf("Printing the list:\n");
    for (i = 0; i < size; i++)
    {
        list[i] = rand() % size;
        printf("%d    ", list[i]);
    }
    printf("\nEnter the key to find it's occurrence: ");
    scanf("%d", &key);
    occur(list, size, 0, key, &count);
    printf("%d occurs for %d times.\n", key, count);
    return 0;
}
 
void occur(int list[], int size, int index, int key, int *count)
{
    if (size == index)
    {
        return;
    }
    if (list[index] == key)
    {
        *count += 1;
    }
    occur(list, size, index + 1, key, count);
}

Program Output

Enter the size of the list: 25
Printing the list:
16    17    9    0    19    24    3    8    12    14    5    20    6    2    11    16    20    17    2    11    16    4    2    3    17
Enter the key to find it's occurrence: 17
17 occurs for 3 times.

Program Explanation

1.  First, an array is created with random elements using the rand() function.

2. To find the occurrences of an element in the list, element at the index 0 in the list is compared with the key and, if matched, the count is incremented by one.

3.  The step 2 is repeated for each element in the list by increasing the value of index by 1 each time.