C++考试

1.程序填空

1.1函数调用

#include 
using namespace std;
class Test
{
public:
	void set(char ch)
	{
		c = ch;
	}
	void show()
	{
		cout << "char in Test is:" << c << endl;
	}
private:
	char c;
};
int main()
{
	Test test1,test2;
	test1.set('a');
	test2.set('b');
	test1.show();
	test2.show();
	return 0;
}

1.2前置和后置“++”、“–”运算符重载

模板就是这样，具体根据题目要求

point& operator++(){
//前置运算符，需要引用返回，不需要参数。返回自增后的值
		x++;
		y++;
		return *this;
	}
	point operator++(int){
	//后置++，不需要引用返回，需要参数区分。返回自增前的值
		point temp(x,y); 
		x++;
		y++;
	    return temp;
	}

1.3异常处理

void check(int score)
{
	try
	{
		1.if (score > 100)throw"成绩超高!";
		2.else if (score < 60)throw"成绩不及格!";
		else cout << "the score is OK..." << score << endl;
	}
	3.catch (char* s)
	{
		cout << s << endl;
	}
}
int main()
{
	check(45);
	check(90); 
	check(101);
	return 0;
}

1.4文本文件读取

int main()
{
    char s[100];
    1.fstream infile("f2.dat", ios::in); //定义文件流对象,打开磁盘文件
    2. if (!infile)                                  //如果打开失败,infile 返回0值
    {
        cerr << "打开 f2.dat 文件失败!\n" << endl;
        cerr << "f2.dat 可能不存在，或者文件已损坏，或者没有权限!\n" << endl;
        cerr << "按任意键退出程序...\n" << endl;
        getch();
        exit(1);
    }
   3. while (!infile.eof())
    {
        infile.getline(s, sizeof(s));
        cout << s << endl;
    }
    infile.close();//关闭磁盘文件“f2.dat”
    return 0;
}

2.程序阅读

2.1C++编程基础

#include
using namespace std;
void test1()
{
	const int T = 5;//控制平方根和最大n值
	int i, s = 0;
	for (i = 1; i <= T; i++) 
	{
		s += i * i;//实现平方和
		cout << s << ' ';
	}
	cout << endl;
}
int main()
{
	test1();
}

2.2继承与派生

class A 
{
	int a;
public:
	A(int aa = 0) { a = aa; cout << "A():" << a << endl; }
};
class B :public A {
	int b;
public:
	B(int aa = 0, int bb = 0) : A(aa) { b = bb; cout << "B():" << b << endl; }
};
int main() 
{
	B x(5), y(6, 7);
	return 0;
}

2.3静态成员

class CTest {
public:
	CTest(int iVar) :m_iVar(iVar) { m_iCount++; }
	~CTest() { }
	void Print()const;
	static int GetCount() { return m_iCount; }
private:
	int m_iVar;
	static int m_iCount;
};
int CTest::m_iCount = 0;
void CTest::Print()const
{
	cout << this->m_iVar << " " << this->m_iCount << " ";
}
int main() {
	CTest oTest1(6);
	oTest1.Print();
	CTest oTest2(8);
	oTest2.Print();
	cout << CTest::GetCount();
	return 0;
}

定义了一个名为CTest的类，该类具有一个整数成员变量m_iVar和一个静态整数成员变量m_iCount。它还定义了一个构造函数，该构造函数使用初始化列表初始化成员变量，并将静态成员变量递增1。它还定义了一个析构函数和一个名为Print()的公共成员函数，该函数打印对象的成员变量值和静态成员变量值

2.4继承与派生

class Base {
private: int Y;
public:
	Base(int y = 0) { Y = y; cout << "Base(" << y << ")\n"; }
	~Base() { cout << "~Base()\n"; }
	void print() { cout << Y << " "; }
};
class Derived :public Base {
private: int Z;
public:
	Derived(int y, int z) :Base(y)
	{
		Z = z; cout << "Derived(" << y << "," << z << ")\n";
	}
	~Derived() { cout << "~Derived()\n"; }
	void print() { Base::print(); cout << Z << endl; }
};
int main() {
	Derived d(10, 20); d.print();
	return 0;
}

2.5 输入输出

#include
using namespace std;
int main()
{
	cout.flags(ios::oct);
	cout << "OCT:161=" << 161 << endl;
	cout.flags(ios::dec);
	cout << "DEC:161=" << 161 << endl;
	cout.flags(ios::hex);
	cout << "Hex:161=" << 161 << endl;
	cout.flags(ios::uppercase|ios::hex);
	cout << "UPPERCASE:161=" << 161 << endl;
	return 0;
}

输入输出知识点

2.6 模板

#include
#include
using namespace std;
template
//声明函数模板
T myMax(T x, T y) {
    cout << "This is a template function! max is:";
    return x > y ? x : y;
}
const char* myMax(const char* x, const char* y) {  //重载的普通函数
    cout << "This is the overload function with char*,char*! max is:";
    return strcmp(x, y) > 0 ? x : y;
}
//重载的普通函数
int myMax(int x, int y) {
    cout << "This is the overload function with int, int! max is:";
    return x > y ? x : y;
}
int myMax(int x, char y) { //重载的普通函数
    cout << "This is the overload function with int,char! max is;";
    return x > y ? x : y;
}
int main() 
{
    const char* s1 = "Beijing 2008", * s2 = "Welcome to Beijing!";
    cout << myMax(2, 3) << endl;//调用重载的普通函数:int myMax(int x;int y)
    cout << myMax(2.0, 3.0) << endl;//调用函数模板,此时T被 double 取代
    cout << myMax(s1, s2) << endl; //调用重载的普通函数 :char* myMax(char * x,char* y)
    cout << myMax(2, 'a') << endl;//调用重载的普通函数:int myMax(int x，char y)
    cout << myMax(2.3, 'a') << endl; //调用重载的普通函数:int myMax(int x，char y)
    return 0;
}

3.程序改错

3.1三种访问权限

#include
using namespace std;
class T {
protected:             //protected 改为 public 类和对象 
	int p;
public:
	T(int m) { p = m; }
};
int main() {
	T a(10);
	cout << a.p << endl;
}

3.2 友元

#include
using namespace std;
class Date;
class Time {
public:
	Time(int h, int m, int s) { hour = h; minute = m; sec = s; }
	void show(Date& d);
private:
	int hour, minute, sec;
};
class Date {
public:
	Date(int m, int d, int y) { month = m, day = d, year = y; }
	void Time::show(Date&);//应当改为友元函数在前面加friend，
	否则show函数将无法访问Date类的私有变量
private:
	int month, day, year;
};
void Time::show(Date& d) {
	cout << d.month << "-" << d.day << "-" << d.year << endl;
	cout << hour << ":" << minute << ":" << sec << endl;
}
int main() {
	Time t1(9, 23, 50);
	Date d1(5, 1, 2023);
	t1.show(d1);
	return 0;
}

3.3抽象类不能实例化对象

#include
using namespace std;
class CBase {
public:
	CBase(int iBase = 0) :m_iBase(iBase) {}
	virtual void Show() = 0;
	int Get() const { return m_iBase; }
private:
	int m_iBase;
};
class CDerive :public CBase {
public:
	CDerive(int iBase = 0, int iDerive = 0) :CBase(iBase)
	{
		m_iDerive = iDerive;
	}
	void Show()
	{
		cout << CBase::Get() << "," << m_iDerive << endl;
	}
private:
	int m_iDerive;
};
int main() {
	CBase obj(10);//虚函数不能初始化成员变量
	因此应当改为CDerive（10）
	obj.Show();
	return 0;
}

3.4常数据成员初始化必须使用构造函数的初始化列表

#include
using namespace std;
class CTest {
public:
	CTest(int iVar = 0) { m_iVar = iVar; }
	//初始化const修饰的成员变量
	//CTest(int iVar = 0):m_iVar(iVar）
	{};
	void Print()const { cout << m_iVar << endl; }
private:
	const int m_iVar;
};
int main() {
	const CTest oTest(13);
	oTest.Print();
	return 0;
}

3.5以引用传递的方式向函数传递对象

#include
using namespace std;
void swap(int& a, int& b)
{
	int tmp; tmp = a; a = b; b = tmp;
}
int main()
{
	int a = 19, b = 15;
	cout << "a=" << a << "," << "b=" << b << endl;
	swap(&a, &b);                //swap（a,b)引用传递
	cout << "a=" << a << "," << "b=" << b << endl;
	return 0;
}

4.程序设计

4.1运算符重载

#include 
using namespace std;
class Point {
	private:
		int x;
		int y;
	public:
		Point(int x1 = 0, int y1 = 0) : x(x1), y(y1) {}
		void show();       
		friend Point operator+(const Point &, const Point & );
		friend Point operator-(const Point &, const Point & );
};
/*！！！三个成员函数的定义！！！*/ 
void Point::show() {
	cout << "(x,y) = " << "(" << x << "," << y << ")" << endl;
}

Point operator+(const Point &a1, const Point &a2) {
	return Point(a1.x + a2.x, a1.y + a2.y);
}

Point operator-(const Point &a1, const Point &a2) {
	return Point(a1.x - a2.x, a1.y - a2.y);
}
int main()
{
	Point a1(1, 2);
	Point a2(4, 5);
	Point a;
	a = a1 + a2;
	cout << "a: ";
	a.show();
	a = a1 - a2;
	cout << "a: ";
	a.show();
	return 0;
}

4.2多态的程序实现方法

#include
using namespace std;
class Shape { 
	public:
		virtual double getArea () = 0;	
};
/*！！！！  Rectangle类的定义   ！！！！！*/
class Rectangle: public Shape { 
	public :
		Rectangle(double x, double y): length(x), width(y) {
		}
		double getArea() {
			return length * width;
		}
	private:
		double length, width;
};
/*！！！！  Circle类的定义   ！！！！！！*/
class Circle: public Shape { 
	public :
		Circle(double r): R(r) { 
		}
		double getArea() {
			return 3.14 * R * R;
		} 
	private:
		double R;
};

int main() {
	Shape *rect = new Rectangle(2, 3);
	cout << rect->getArea() << endl;
	Shape *circle = new Circle(2);
	cout << circle->getArea() << endl;
	delete rect;
	delete circle;
	return 0;
}