Why do I getting this error

Question

https://code.sololearn.com/c5EAAtJEJ2jF/?ref=app

Answer 1

FF9900 " Console doesn't contain a deflation for ToDouble " it gives this error when I run the code

Answer 2

Console class has ReadLine, WriteLine methods for console related operations.
Convert class has methods to convert from string to primitive types toInt, toDouble, ... That's what @FF9900 telling..

Answer 3

double radius = Convert.ToDouble(Console.ReadLine()) ;