input: Write a python function to print a square pattern of a given size using asterisks.
  assert print_square_pattern(3) == '***\n***\n***\n'
  assert print_square_pattern(2) == '**\n**\n'
  assert print_square_pattern(1) == '*\n'
  assert print_square_pattern(4) == '****\n****\n****\n****\n'
output: def print_square_pattern(size):
      pattern = ''
      for i in range(size):
          pattern += '*' * size + '\n'
      return pattern