input: Write a function to count the number of vowels in a string. The function should return the total count of vowels (both uppercase and lowercase) in the given string. Return 0 if the string is empty.
  
  assert count_vowels("Hello, World!") == 3
  assert count_vowels("Python Programming") == 4
  assert count_vowels("AEIOUaeiou") == 10
  assert count_vowels("Grzzly") == 0
  assert count_vowels("") == 0
output: def count_vowels(s):
      vowels = "aeiouAEIOU"
      count = 0
      for char in s:
          if char in vowels:
              count += 1
      return count