clear;
clc;

s = input("Enter r? ", "s");
r = str2num(s);
if isempty(r) 
    disp(s + " is not a number.");
else
    if r > 0
        A = r * r * pi;
        disp(A);
    else
    %     disp("Not a circle.");
        disp(r + " is negative.");
    end
end