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Seems most of them make the same mistake that Sundial was warning about: a long is not guaranteed to be large enough on all platforms. unsigned long long should be good for 19 digits however, but as Sundial says, why limit yourself: process the number as a string.
Also: when this is not “a learning exercise,” remember that there are many contributed libraries of software … for every programming language that exists … where other(!) people have confronted these “problems that we all have,” and solved them very well. Including all(!) variations of “credit-card number validation.”
It’s very important to realize, when you are first “learning to program in [X],” that today you are not “alone.” Extremely the opposite. Therefore, when you confront any problem, your first assumption should be that someone else has already done it. (And that you can freely “sneak a peek” at their source code. In due time, you might make your own contribution …)
Last edited by sundialsvcs; 02-06-2024 at 10:37 PM.
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