creating variable from two others

[cuboctahedron]

Hi,

I am trying to populate a combobox(ComboCities) to display cities dependant on the selection of another combobox (ComboCountries).
Since the list of countries come from a database, and expand over time, I want to use the CountryID-value to determine which array must be read to
populate the ComboCities.

Currently I do the following:

//populating country data
countries="England|France|Germany";
countriesID="1|2|3";

//loading all cities: note-> every arrayname contains the countryID
cityname1="London|Leeds|Liverpool|Glasgow";
citiesID1="11|12|13|14";
cityname2="Paris|Lyon|Marseille|Lille";
citiesID2="15|16|17|18";

//function to populate the ComboCities
function getcities ()
{
countryid=CombCountries.getValue();
ComboCities.removeAll();
NewIDs="citiesID"+countryid;
NewName="cityname"+countryid;

listcityids=NewIDs.split("|");
listcitynames=NewName.split("|");
for (i=0; i<listcityids.length;i++) {ComboCities.addItemAt(i,listcitynames[i], listcityids[i]);}
}

Somehow the arrays 'listcityids' and 'listcitynames' are not created. I found a workaround that will create these arrays by
changing the following codepart:

NewIDs=eval("citiesID"+countryid);
NewName=eval("cityname"+countryid);

So my question really is:
Why I had to use the eval() function for this?(why does it technically changes the logic of the code)

I hope someone can explain it, because I had to add code, without knowing the true purpose.

Kind regards
Patrick