Home Exc. #1 - Find occurrences in range

#include <stdio.h>
#include <stdlib.h>

int* numbersInRange(int a, int b, int k, int d, int * pSize);
int countDigits(int num, int d);

int main()
{
    int a = 1, b = 100, k = 1, d = 3, size = 0;

    int* arr = numbersInRange(a, b, k, d, &size);

    if (arr == NULL)    // Allocation failed
    {
        printf("\nAllocation failed.\n\n");

        return 1;
    }

    printf("\nThe number %d will appear exactly %d time%s in %d numbers from %d to %d\n\n", d, k, (k < 2) ? "" : "s", size, a, b);

    for (int i = 0; i < size; i++)
        printf("%d%s ", arr[i], (i==size-1) ? "." : ",");

    printf("\n");

    free(arr);

    return 0;
}

int* numbersInRange(int a, int b, int k, int d, int * pSize)
{
    int size = 0;

    for (int i = a; i <= b; i++)
    {
        if (countDigits(i, d) == k)
            size++;
    }

    int* ptr = (int*)malloc(size * sizeof(int));

    if (ptr == NULL)    // Allocation failed
    {
        *pSize = 0;

        return NULL;
    }

    int z = 0;

    for (int i = a; i <= b; i++)
    {
        if (countDigits(i, d) == k)
                ptr[z++] = i;
    }

    *pSize = size;

    return ptr;
}

int countDigits(int num, int d)
{
    int count = 0;

    while (num != 0)
    {
        if (num % 10 == d)
            count++;

        num /= 10;
    }

    return count;
}