input: Write a function that prompts the user to enter the value of radius to calculate the area of a circle. The function should return the calculated area.
  assert calculate_circle_area("5")==78.5
  assert calculate_circle_area("2.5")==19.625
  assert calculate_circle_area("0")==0.0
  assert calculate_circle_area("-3")==28.26
  assert calculate_circle_area("abc")==None
output: def calculate_circle_area(radius):
      try:
          r = float(radius)
          return 3.14 * r * r
      except ValueError:
          return None