c how to program 习题2.20

//c how to program 习题2.20
#include <stdio.h>

int main(void)
{
	int r;

	printf("请输入半径：");
	scanf("%d", &r);

	printf("直径是：%d\n", r*2);
	printf("周长是：%f\n", 2*3.14159*r);
	printf("面积是：%f\n", 3.14159*r*r);
}