What does the letter A(a) stand for?

Question

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Sorry, what does the letter A (or a) stand for in the strconv.Atoi() or strconv.Itoa() conversion?
But what does the letter A/a mean in the "string-to-int" and "int-to-string" conversion methods?
Normal people want to understand this, but for some reason it is not explained anywhere.

Answer 1

https://ru.wikipedia.org/wiki/Atoi