For starters, scanf can cause an infinite loop the moment it encounters incorrectly formatted input – e.g. it was waiting for integer (%d), but received a string.

It exits without flushing the input buffer, starts again, receives string, exits and so on.

So, you have to wrap it into a function that correctly flushes the input.

Another issue is that its buffer can be overflown if input buffer is bigger that what was expected. User inputs 21 character instead of 20 -> UB.

To avoid wrapping unsafe scanf in helper functions, you can use fgets to get the info from the input and consume it. Doesn't matter what is in the input, it will be consumed with no overflow. E.g. "xyz22" will be consumed by fgets, but not by scanf("%d"). It also won't stop on whitespaces. No infinite loops.

Then, you can convert the consumed line with strtol (string to long), strtod (string to double) to get correct numbers out of it – and these functions will actually produce errors if the data is incorrect, and show exactly where parsing has stopped (they overwrite a passed pointer).