namespace，缺省参数，函数重载，引用，内联函数的用法

namespace 用法

#include 
namespace China    // 1
{
	double population = 14.5;
	double GDP = 17.8;
	namespace Shanghai     // 2
	{
		double population = 0.56;
		double GDP = 1.25;
	}
}

namespace USA
{
	double population = 3.25;
	double GDP = 25.4;
	namespace NewYork
	{
		double population = 0.32;
		double GDP = 2.34;
	}
}

namespace Japan
{
	double population = 1.1;
	double GDP = 8.3;
	namespace Tokyo
	{
		double population = 0.43;
		double GDP = 1.9;
	}
}

using namespace Japan;    // 3
using std::cout;     //4 

int main()
{
	cout << "中国的人口与经济总量：" << std::endl;   //5
	cout << China::population << " " << China::GDP << std::endl;    // 6
	cout << "中国上海的人口与经济总量：" << std::endl;
	cout << China::Shanghai::population << " " << China::Shanghai::GDP << std::endl;  //7
	cout << "美国的人口与经济总量：" << std::endl;
	cout << USA::population << " " << USA::GDP << std::endl;
	cout << "美国纽约的人口与经济总量：" << std::endl;
	cout << USA::NewYork::population << " " << USA::NewYork::GDP << std::endl;
	cout << "日本的人口与经济总量：" << std::endl;
	cout << population << " " << GDP << std::endl;   //8
	cout << "日本东京的人口与经济总量：" << std::endl;
	cout << Tokyo::population << " " << Tokyo::GDP << std::endl;    //9
	return 0;
}

缺省参数 用法

test.h

int TotalPrice(int NumberOfPeople, int AdmissionFee = 20);  // 1  

test.cpp

#include 
#include "test.h"
using namespace std;

int TotalPrice(int NumberOfPeople, int AdmissionFee)  // 2
{
	return NumberOfPeople * AdmissionFee;
}

int main()
{
	char IsStudent = 0;
	int NumberOfPeople = 0;
	cout << "你是学生吗(Y/N)：";
	cin >> IsStudent;
	if (IsStudent == 'Y')
	{
		cout << "请输入旅游人数：";
		cin >> NumberOfPeople;
		cout << TotalPrice(NumberOfPeople, 10);
	}
	else
	{
		cout << "请输入旅游人数：";
		cin >> NumberOfPeople;
		cout << TotalPrice(NumberOfPeople);
	}
	return 0;
}

函数重载 用法

#include 
using namespace std;

void Add(int a, int b)   // 1
{
	cout << a + b << endl;
}

void Add(double a, int b)   // 2
{
	cout << a + b << endl;
}

void Add(int a, double b)   // 3
{
	cout << a + b << endl;
}

void Add(double a, double b)
{
	cout << a + b << endl;
}

void Add(int a, int b, int c)  // 4
{
	cout << a + b + c << endl;
}

int main()
{
	Add(1, 2);
	Add(1.1, 2);
	Add(2, 3.3);
	Add(1.1, 3.5);
	Add(1, 2, 3);
	return 0;
}

引用 用法

#include 
using namespace std;

void Swap(int& a, int& b)    // 1 
{
	int tmp = a;
	a = b;
	b = tmp;
}

void Print(const double& a, const double& b)    // 2
{
	cout << a << " " << b << endl;
}

int main()
{
	int x = 10;
	int y = 20;
	Swap(x, y);
	cout << x << " " << y << endl;

	int m = 100;
	int n = 200;
	Print(m, n);
	return 0;
}

内联函数

#include 
using namespace std;

inline void add(int& a)    //  1  2(声明与定义不能分开)
{
	a++;
}

int main()
{
	int x = 0;
	for (int i = 0; i < 100000000; i++)
	{
		add(x);
	}
	cout << x << endl;
	return 0;
}