用c语言编写函数,求圆的周长和面积,用函数.急求.

#include
#define PI 3.1415926
double area(double r)
{
return PI * r * r;
}
double perimeter(double r)
{
return 2 * PI * r;
}
int main()
{
printf("请输入半径的值:\n");
double r;
scanf("%lf",&r);
printf("周长为%lf\n",perimeter(r));
printf("面积为%lf\n",area(r));
return 0;
}