c++ 基礎之 namespace_quote

#include <stdlib.h>
#include <iostream>
using namespace std;
//標準命名空間（包含很多標準的定義）
//standard
/*using namespace std;
//命名空間類似於java中的包(歸類)


//自定義命名空間
namespace NSP_A{
int a = 9;
}
namespace NSP_B{
int a = 18;
//命名空間嵌套
namespace NSP_C{
int a = 22;
}
}
void main(){


printf("this is c in c plus\n");
//std:cout << "this is c plus_plus" << std:: endl;
     cout << "this is c plus_plus" << endl;


cout << NSP_A::a<< endl;
cout << NSP_B::a << endl;
cout << NSP_B::NSP_C::a<< endl;
getchar();
}*/
/* #define PI 3.14
//類 圓
class Mcircle{
//屬性(共用訪問權限修飾符)
private:
double r;
double s;
    public : 
void setR(double r){
this->r = r;
}


double getS(){
return PI*r*r;
}
};


void main(){
Mcircle c1;
c1.setR(4);
std::cout << "原型面積：" << c1.getS() << std::endl;
getchar();
}
*/
/*結構體
struct MyTeacher{


public :
char name[20];
int age;


public :
void say(){
cout << this->age << "歲" << endl;
}




};


void main(){
MyTeacher t;
t.age = 18;
t.say();
getchar();
}*/




/*
void main(){
//布爾類型
bool isSingle = true;
if (isSingle){
cout << "單身" << endl;
}
else{
cout << "有對象" << endl;

}
//三目運算符可以作爲左值
int a = 10; int b = 20;
((a > b) ? a : b) = 99;
cout << "b="<<b<< endl;


getchar();



}


*/
/*
//引用
void main(){
//變量名-門牌號（內存空間0x-00001的別名）
int a = 10;
//b就是這個內存空間的別名  &在c++中代表引用
int &b = a;
int* c = &a;
b = 55;  //修改了地址上的值  b = 55  *c =55;
cout << b << endl;
cout << *c << endl;
getchar();


}
*/


void swap_p(int* a,int* b){
int c = 0;
c = *a ;
*a =*b;
*b = c;
}


//引用的用處
void  swap_u(int &a,int &b){
int c = 0;
c = a;
a = b;
b = c;
}


void main(){
int x = 10;
int y = 20;
printf("%d,%d\n",x,y);
int* xp = &x;
int* yp = &y;
swap_p(xp,yp);
printf("%d,%d\n", x, y);
swap_u(x, y);
printf("%d,%d\n", x, y);
getchar();
}