Implementation of Sieve of Eratosthenes Algorithm in C

[Sly Guy]

Okay, so this function I created uses the Sieve of Eratosthenes algorithm to compute all the primes <= n. This function stores the prime numbers and the count of primes in the parameters. When the function exits, primes should be pointing to a chunk of dynamically allocated memory that holds all the primes <= num. *count will have the count of primes.

void getPrimes(int usernum, int* count, int** array){
	(*count) = usernum - 1;
	int sieve[usernum-1], primeNums = 0, index, fillnum, multiple;
	
	
	
	//Fills the array with the numbers up to the user's ending number, usernum.

	for(index = 0, fillnum = 2; fillnum <= usernum; index++, fillnum++){
		sieve[index] = fillnum;
	}
	



	 /*Starts crossing out non prime numbers starting with 2 because 1 is not a prime. 
         It then deletes all of those multiples and moves on to the
         next number that isnt crossed out, which is a prime. */

	 int j = 0;
	 for (; primeNums < (usernum - 1); ++primeNums, j++)	//Walks through the array.
        {

			if (sieve[j]){	  //Checks if that number is NULL which means it's crossed out
			
                   for (multiple = (sieve[j])*2; multiple < usernum; multiple = multiple + (sieve[j])) 
                   //If it is not crossed out it starts deleting its multiples.
                   {

                        if (sieve[multiple]) {     
        //Crossing multiples out and decrements count to move to next number
							*(sieve + multiple) = 0;
                            --(*count);
                           }
                   }
            }
        }
        *array = malloc((sizeof(int) * (*(count + 1))));
		 assert(*array);
        (*array) = sieve;
        int i =0;
        for(;i<usernum;i++){
			if(sieve[i] != NULL)
			printf("%d ", sieve[i]);
		}
        
        
}

Now, here is the intended output and my output. As you can see, something is wrong within my getPrimes function but I am unsure as to what.

Intended Output:

There are 8 prime numbers less than or equal to 19

2 3 5 7 11 13 17 19

My Output:

2 3 4 5 7 9 13 15 19

Can anyone spot where I went wrong? I'm dying to figure out what I am missing it feels like I'm so close, this is a HW question, but I wrote all this code the instructions were basically what was at the top and I had to start completely fresh.

I'd truly appreciate any help that can be giving.

Thank you in advance,
Sly Guy