>can we really create arrays with an unspecified number of entries and fill in every other entry Seems that was a typo, but you can do that in some languages,

>can we really create arrays with an unspecified number of entries and fill in every other entry Seems that was a typo, but you can do that in some languages, either directly (Perl, PHP) or with help (many others). "Autovivification" seems to be the term: https://en.wikipedia.org/wiki/Autovivification https://en.wikipedia.org/wiki/Autovivification