input: Write a function to reverse a given string. If the input string is empty, return an empty string. Use a loop to iterate through the string and build the reversed string.
  
  def reverse_string(input_string):
      reversed_string = ""
      for i in range(len(input_string)-1, -1, -1):
          reversed_string += input_string[i]
      return reversed_string
  
  assert reverse_string("Python") == "nohtyP"
  assert reverse_string("Hello World") == "dlroW olleH"
  assert reverse_string("") == ""
output: def reverse_string(input_string):
      reversed_string = ""
      for i in range(len(input_string)-1, -1, -1):
          reversed_string += input_string[i]
      return reversed_string