input: Write a python function to compare two strings for equality character by character.
  assert compare_strings("hello", "hello") == True
  assert compare_strings("hello", "world") == False
  assert compare_strings("test", "testing") == False
  assert compare_strings("Python", "python") == False
output: def compare_strings(str1, str2):
      if len(str1) != len(str2):
          return False
      for i in range(len(str1)):
          if str1[i] != str2[i]:
              return False
      return True