I'll start with, I meant no disrespect with my post. (Like leading with, "No offense, but..." which usually means just the opposite. Please take my comments with a grain of salt.)
However, I did not take from Ben's post that the specifications excluded order of operations for the mathematical formula. He was asked to process a dynamic simple math expression in a SELECT statement, restricted to addition, subtraction, multiplication and division.
Ben actually states:
I will pause here and acknowledge that I could have set a precedence to process certain operators first. Or I could have used brackets to control which operations should go together. I decided I didn’t really want to go there. Instead I decided I just needed a charindex that would give me the last occurrence of the operator.
I would suggest, however, that precedence is not an optional component and that without properly including it, you risk incorporating a rather large logical flaw in whatever system this finds as its home. As it's not for my customer, I clearly have no dog in the fight and am not in a position to properly evaluate the impact. Maybe it is truly not a big deal.
I do think the reverse charindex function would be useful and the approach taken was novel. Ultimately, we are also dealing with a posting complied by a very bright guy that was sent out via email subscription to a large group of very bright guys. Eliciting commentary and constructive criticism is part of the reason to post something like this. Take, for example, @negak's modification to the work Ben did to setup order of operations.
Happy coding and Ben - thanks for being willing to post and bear the communities commentary (good and bad).
-wbw