import java.util.Scanner; public class Main{ public static void main(String []args){ Scanner sc = new Scanner(System.in); double a = sc.nextDouble(); double pi = 3.14159; System.out.printf("%.6f",a * 2 * pi); System.out.println(); System.out.printf("%.6f",a * a * pi); } }这题考察对浮点数的计算,
System.out.println();这个就是换行,根据题目的输出结果来打印。