input: Write a function to count the total number of vowels in a given string. If the string is empty then return 0. Vowels are considered as the characters 'a', 'e', 'i', 'o', 'u' in both uppercase and lowercase.
  assert count_vowels("Hello World") == 3
  assert count_vowels("Python Programming") == 4
  assert count_vowels("Quick Brown Fox Jumps Over The Lazy Dog") == 11
  assert count_vowels("aeiouAEIOU") == 10
  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