Handling Edge Cases

I see you're using regex in there. Couldn't you just regex to see if some kind of invalid mix occurs? You could maybe create a list of invalid combos, maybe even a dictionary, if they are always pairs...

Ausgrindtube , could you please elaborate? You see, errors can be of innumerable types, and there are tends-to-∞ chemical reactions thereby making it nearly impossible to create a dictionary of them...

I'm not a chemical scientist and it's been like 30 years since I was in school doing chemistry, so excuse my ignorance. What I was thinking: if you identify in either half of your equation, in your example: Fe or Al, which you could do with regex, then, you could run it through a loop looking for any possible invalid mix, as soon as it finds this, it can stop and output that its invalid. Yeah, you'll have to create a list of all possible elements and then another list or multiple lists of invalid options. I don't think there's any easier way* - it's not like a program can think for itself and know what's invalid. *there are way smarter people here than I am. Maybe they'll find your thread and offer their opinions. You can also search the code playground, the forum or places like github for maybe similar approaches. https://www.sololearn.com/discuss/2337875/?ref=app https://www.sololearn.com/discuss/3173656/?ref=app Here's what I found with edge cases... perhaps not the best subject heading.

Ausgrindtube , thank you. I guess, lets just hope that the user will enter a chemically valid equation...