int readAnimals(const char* filename, ANIMAL* animalPtr, int nrAnimals){
/* pre    :
 * post   : If file contains enough Animals, nrAnimals Animals are read into animalPtr.
 *          If less animals than nrAnimals exist, all animals from the file are read into animalPtr.
 * returns: Nr of animals written into animalPtr or -1 if an error occurs
 */
    int returnValue;
    FILE* f = fopen(filename, "r");
    if ( !f || animalPtr == NULL || nrAnimals <= 0)
    {
        if (!f)
            return -1;
        else
        {
            fclose(f);
            return -1;
        }
    }
    else
    {
        fseek(f, 0, SEEK_END);
        int fileSize = ftell(f);
        int nrAnimalsInFile = fileSize/sizeof(animalPtr);
        fseek(f, 0, 0);
        if (fileSize > 0)
        {
            if (nrAnimalsInFile > nrAnimals)
            {
                for (int i = 0; i<nrAnimals; i++){
                    fread(&animalPtr[i], sizeof(ANIMAL), 1, f);
                }
                returnValue = nrAnimals;
            }
            else
            {
                for (int i = 0; i<nrAnimalsInFile; i++){
                    fread(&animalPtr[i], sizeof(ANIMAL), 1, f);
                }
                returnValue = nrAnimalsInFile;
            }
        }
        else
        {
            fclose(f);
            return -1;
        }
    }


    fclose(f);
    return returnValue;
}