Counting a’s (3)

Write a function @count_a(s, stop)@ that given a string @s@ and a character @stop@ returns the number of times that letter @a@ occurs in @s@ before the first appearance of character @stop@. If character @stop@ is not in @s@, the function must return $-1$ .

Sample session

Problem information

Author: ProAl

Generation: 2026-01-25T16:56:21.451Z