What should i do if i want to change to this method

Question

https://code.sololearn.com/cQslRC7uC87y/?ref=app
Circle a = new Circle(2);
Circle b = new Circle(3);

Answer 1

public Circle(int radius)
{
this.Radius = radius;
}

If radius shall be optional, you can add another constructor without arguments or:

public Circle(int radius = 1)
{
this.Radius = radius;
}

Answer 2

Kyrene the constructors do not accept an argument and collapse and defining the radius' fails.