第七章课本例题

例题1：

/*************************************************************
****    7_1输入圆半径，求圆周长圆面积和球体积    ****
**************************************************************/ 

# include<iostream>
using namespace std;
# define PI 3.1415926

int main()
{
	double perimeter, area, radius, volume;
	cout<<"input redius: ";
	cin>>radius;
	perimeter = 2 * PI * radius;
	area = PI * radius * radius;
	volume = 4.0 / 3.0 * PI * radius * radius * radius;
	cout<<"perimeter = "<<perimeter
		<<" area = "<<area
		<<" volume = "<<volume<<endl;

	return 0;
}

例题3：

/********************************************
****    7_3计算圆面积    ****
*********************************************/

# include<iostream>
using namespace std;

# define PI 3.1415926
# define S(r) PI * r * r

int main()
{
	float radius = 3.6f, area;
	area = S(radius);
	cout<<"radius = "<<radius<<"\t\tarea = "<<area<<endl;

	return 0;
}