test1_13.txt

linux under the C programming which complementary with the book of <linux under the C programming

/*输入一个圆的半径，求出它的面积*/
#include “stdio.h”
#define  PI  3.1415926
#define  area(r)  PI*r*r
main()
{
	float  r,a;
 	scanf(“%f”,&r);
 	a=area(r);
 	printf(“The area is %f”,a);
}