Counting a's (3) X55221

Statement

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

>>> count_a('naturally', 'u')
1
>>> count_a('russian', 't')
-1
>>> count_a('adaptation', 'a')
0
>>> count_a('adaptation', 'n')
3

Information

Author: ProAl
Language: English
Official solutions: Python
User solutions: Python