4) PROGRAM HINH TRON; 
{Nhap ban kinh R cua duong tron. Tinh chu vi, dien tich cua duong tron ay} 
VAR R:real; 
BEGIN 
Write('Nhap ban kinh R: ');readln(R); 
Writeln; 
If R>0 then 
begin 
Writeln('Chu vi P = ',2*pi*R:6:2); 
Writeln('Dien tich S = ',pi*R*R:6:2); 
end 
Else writeln(#7,'Khong thuc hien vi R <= 0'); 
Readln 
END.