Write a Python function to reverse a string without using any built-in functions or slicing.

 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

# Test the function

my_string = "Hello, World!"

reversed = reverse_string(my_string)

print(reversed) #output !dlroW ,olleH