#include
#define PI 3.1415926
double area(double r)
{
return PI * r * r;
}
double perimeter(double r)
{
return 2 * PI * r;
}
int main()
{
printf("請(qǐng)輸入半徑的值:\n");
double r;
scanf("%lf",&r);
printf("周長(zhǎng)為%lf\n",perimeter(r));
printf("面積為%lf\n",area(r));
return 0;
}