input: Write a function to calculate the area of a circle given its radius. The function should return the area rounded to two decimal places. If the radius is not provided or is negative, the function should return 0.
  assert area_circle(5)==78.54
  assert area_circle(-2)==0
  assert area_circle(0)==0
  assert area_circle(3.5)==38.48
  assert area_circle(10)==314.16
output: def area_circle(radius=None):
      if radius is None or radius < 0:
          return 0
      area = 3.14159 * radius * radius
      return round(area, 2)