/*-------------------------------------------------------
功能:输入一个圆半径(r),当r>=0时,计算并输出圆的面积(area)和周长(circumference),否则,输出提示信息。
--------------------------------------------------------*/
#include <stdio.h>
#define PI 3.14 
main()
{ 
	float r,s,l;
	printf("please input r:\n");
	scanf("%f",&r);
	if (r>=0)
	{
/**********Program**********/
	s = PI * r*r;
	l = 2*PI*r;

/**********  End  **********/
		printf("the area is %f\n",s);        
		printf("the circumference is %f\n",l);
	}
	else
		printf("input error!\n"); 
}