input: Write a function to iterate over a list of numbers and print only the even numbers. If the list is empty, print "No numbers to check."
  
  assert print_even_numbers([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])
  assert print_even_numbers([1, 3, 5, 7, 9])
  assert print_even_numbers([])
output: def print_even_numbers(numbers):
      if not numbers:
          print("No numbers to check.")
      else:
          for num in numbers:
              if num % 2 == 0:
                  print(num)