Question

 int main( ) {

   double radius;

  const double PI= 3.15169;

   double area = radius * radius * PI;

  cout<<"Area is " << area;

return 0:

 }

Answer 1

#include <iostream>
using namespace std;


 int main( ) {


   double radius;
   cout<<"Input radius: ";
   cin>>radius;


  const double PI= 3.15169;


   double area = radius * radius * PI;


  cout<<"Area is " << area;


return 0;


 }