input: Write a python function to calculate the product of two numbers without using the multiplication operator.
  assert product_without_mul(3, 7) == 21
  assert product_without_mul(0, 5) == 0
  assert product_without_mul(5, 0) == 0
  assert product_without_mul(-4, 6) == -24
output: def product_without_mul(a, b):
      result = 0
      positive_b = abs(b)
      for _ in range(positive_b):
          result += a
      
      if b < 0:
          result = -result
      
      return result