Programming exercise 6-4 in book, Pointers on C.

Find_Prime_Number.c

void FindPrimeNumber(int size, int results[]) {
    // create elements array
    int *elements;
    elements = (int *)malloc(size * sizeof(int));
    
    for (int i = 0; i < size ; i++) {
        elements[i] = 1 ;
    }
    
    //start to cross out. Beginning from i = 2
    for (int i = 2; i < size + 2; i++) {
        int j = i * 2;
        while (j < size + 2) {
            elements[j - 2] = 0 ;
            j += i;
        }
    }
    
    // put all prime number into results array
    int counter = 0;
    for (int i = 2; i < size + 2 ; i++) {
        if (elements[i - 2] == 1) {
            results[counter] = i;
            counter++;
        }
    }
}

int main(int argc, const char * argv[]) {
    
    int *results;
    results = (int *)malloc(1000 * sizeof(int));
    for (int i = 0; i < 1000; i++) {
        results[i] = '\0';
    }
    
    FindPrimeNumber(1000, results);
    
    for (int i = 0; i < 1000; i++) {
        if (results[i] == '\0') break;
        printf("Prime number: %d\n", results[i]);
    }
    
    free(results);
    
    return 0;
}