C++命名空间（namespace）

#include <iostream>

using namespace std;


namespace name_space_A
{
    const float PI = 3.14;
    enum tagDAYS{MON, TUE, WEN, THU, FRI, SAT, SUN};
    int i, j, k = 10;
    string str1, str2("Hello");
    int max(int x, int y);
    int min(int x, int y) {return x < y ? x : y; }

    void output()
    {
        cout << name_space_A::k << endl;
    }

    template <typename T>
    int compare(const T& v1, const T& v2)
    {
        return v1 == v2;
    }
    template <class T>
    class TComplex
    {
    public:
        TComplex(){}
        void setdata(T a,T b) {x = a, y = b;}

    private:
        T x, y;
    };

    namespace  name_space_B
    {
        int i , j, k = 11;
        void output()
        {
            cout << name_space_A::j << endl;
        }
    }
}

int main()
{
    cout << "Hello world!" << endl;
    name_space_A::output();
    name_space_A::name_space_B::output();
    return 0;
}