input: Write a function to reverse a given string. If the input string is empty, return an empty string. The function should use a loop to iterate through the string in reverse order and concatenate each character to form the reversed string.
  assert reverse_string("Python") == "nohtyP"
  assert reverse_string("Hello") == "olleH"
  assert reverse_string("") == ""
  assert reverse_string("12345") == "54321"
  assert reverse_string("!@#$%") == "%$#@!"
output: def reverse_string(s):
      reversed_str = ""
      for char in s[::-1]:
          reversed_str += char
      return reversed_str