This is C++ program.
Write a Circle class that has the following member variables:
radius: a double
PI: a double initialized with the value 3.14159. You can define this either as a global variable or a public constant.
The class should have the following member functions:
Default Constructor. A default constructor that sets radius to 0.0.
Constructor. Accepts the radius of the circle as an argument.
setRadius. A mutator function for the radius variable. This function should