Probably biased here, but back in the days before frameworks I found plain PHP with HTTP a good case of explaining, out of necessity. Every variable arrives as

Probably biased here, but back in the days before frameworks I found plain PHP with HTTP a good case of explaining, out of necessity. Every variable arrives as a string anyway and you need to check if it's actually an integer if you want to use it as such (let's ignore weird autocasting). On the other hand I'm not sure it's teaching a good lesson here, because you're simply taking the un-typedness of HTTP parameters as an example, whereas in other environments you would simply explain there are number data types and strings and others...