input: Write a function that prompts the user to enter the value of radius to calculate the area of a circle and then returns the calculated area. If the input radius is negative, the function should prompt the user again until a non-negative value is entered.
  
  def calculate_circle_area():
      Pi = 3.14
      while True:
          radius = float(input("Please enter the radius of the circle: "))
          if radius >= 0:
              area = Pi*radius**2
              print("The area of the circle is:", area)
              return area
          else:
              print("Radius cannot be negative. Please enter a non-negative value.")
  
  assert calculate_circle_area() == 78.5  # Assuming the user inputs 5
  assert calculate_circle_area() == 3.14  # Assuming the user inputs 1
  assert calculate_circle_area() == 0.0  # Assuming the user inputs 0
  assert calculate_circle_area() == 12.56  # Assuming the user inputs 2
output: def calculate_circle_area():
      Pi = 3.14
      while True:
          radius = float(input("Please enter the radius of the circle: "))
          if radius >= 0:
              return Pi * radius ** 2
          else:
              print("Radius cannot be negative. Please enter a non-negative value.")