什么是常量（）

1. const 将变量声明为常量

       const  type-name cinstant -name 

#include

int main()
{
	using namespace std;

	const int Pi = 22.0 / 7;
	cout << "the value of constant Pi is " << Pi << endl;

	return 0;

}

输出：

the value of constant Pi is 3.14286

const double 生命Pi是一个double类型的常量，变成const int 便是一个int 型的常量，不会再被赋值和修改。常量是一种确保不会被修改的强大方式。

2.enum 枚举型常量

有时候变量只能有一组特定的取值

#include 
using namespace std;

enum CardinalDirections
{
	North = 25,
	South,
	East,
	West
};

int main()
{
	cout << "displaying direction and their symbolic values" << endl;
	cout << "North:" << North << endl;
	cout << "South:" << South << endl;
	cout << "East:" << East << endl;
	cout << "West:" << West << endl;

	CardinalDirections WindDirection = South;
	cout << "Variable WinDirect =" << WindDirection << endl;
	return 0;
};

其中CardinalDirections WindDirection = South;   声明了常量WindDirection，其类型是CardinalDirections。这个枚举常量只能取CardinalDirections中的指定值，而不能去其他值；