The following C code will return the array from an array reference.

AV* get_array(SV* aref)
{
    if (! is_array_ref(aref))
        croak("get_array() argument is not an array reference");
    
    return (AV*)SvRV(aref);
}

int is_array_ref(SV* ref)
{
    if (SvROK(ref) && SvTYPE(SvRV(ref)) == SVt_PVAV)
        return 1;
    else
        return 0;
}

SV* get_element(AV* array, int index)
{
    SV   **temp;
    temp = av_fetch(array, index, 0);
    if (!temp) {
        printf("Could not fetch element %d from array", index);
        croak("Ending program");
    }
    else
        return *temp;
}
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Then, in another place in your C code you can use it like this:

    /* dereference array and get requested arrayref */
    array  = get_array(aref);
    elem   = get_element(array, index);
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See AI::NeuralNet::Simple code for more information. I pass array references directly from Perl to C and back to Perl. I use Inline::C to make things easy.