C语言求圆的面积和周长

#define pi 3.1415926  
#include 
int main()
{
	float r,area,perimeter;
	printf("请你输入圆的半径r:\n");
	scanf("%f",&r);
	area=pi*r*r;
	perimeter=pi*r*2;
	printf("直径为:%0.02f\n圆的面积为:%0.03f\n周长为:%0.02f",2*r,area,perimeter);
	return 0;
}