Why is it “bad” to use cin for numeric variables? [closed]

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Posted on 16 Aug 2022, this text provides information on Syllabus Queries related to Course Queries. Please note that while accuracy is prioritized, the data presented might not be entirely correct or up-to-date. This information is offered for general knowledge and informational purposes only, and should not be considered as a substitute for professional advice.

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manpreet Tuteehub forum best answer Best Answer 2 years ago

My current professor states on his syllabus:

"Never use cin >> to read directly into a numeric variable, like int or double or float. Read as a string (C or C++) and convert to a number using atoi or atof."

Is there a reason for this? At first I thought it is to avoid fail flags but if you just add input validation code isn't it fine to "cin >> myInt"?

Using his method, if they entered "4a5" and I did atoi wouldn't it still throw an error?

Thanks~

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manpreet 2 years ago

In general, there is nothing wrong with it at all. This advice would seem to be wrong.

In fact, by relying solely on stoi and friends, you lose any ability to control the conversion process. You might want to use these in some very domain-specific cases where you want to extract a specific number of characters and then attempt to convert them, but that's down to business logic.

Certainly, relying on antiquated code like atoi is even worse, what with its undefined behaviour on encountering many failure cases.


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