input: Write a python function to compare two strings and count the number of differing characters.
  assert compareStrings('python', 'perl') == 3
  assert compareStrings('hello', 'hello') == 0
  assert compareStrings('abcdef', 'abcxyz') == 3
  assert compareStrings('short', 'longer') == 1
output: def compareStrings(str1, str2):
      diff_count = 0
      for s1, s2 in zip(str1, str2):
          if s1 != s2:
              diff_count += 1
      diff_count += abs(len(str1) - len(str2))
      return diff_count