input: Write a python function to calculate the power of a number using iteration.
  assert power_of(2, 5) == 32
  assert power_of(3, 3) == 27
  assert power_of(5, 0) == 1
  assert power_of(7, 2) == 49
output: def power_of(base, exponent):
      result = 1
      for _ in range(exponent):
          result *= base
      return result