C++Primer Plus笔记——第十二章 类和动态内存分配课后编程练习答案

目录

课后习题

习题1

习题2

习题3

习题4

习题5&6

---

课后习题

习题1

#include 
#include 

using namespace std;

class Cow 
{
	char name[20];
	char * hobby;
	double weight;
public:
	Cow();
	Cow(const char * nm, const char * ho, double wt);
	Cow(const Cow & C);
	~Cow();
	void ShowCow() const;
};

Cow::Cow() {}

Cow::Cow(const char * nm, const char * ho, double wt)
{
	strcpy(name, nm);
	hobby = new char[strlen(ho) + 1];
	strcpy(hobby, ho);
	weight = wt;
}

Cow::Cow(const Cow & C)
{
	strcpy(name, C.name);
	hobby = new char[strlen(C.hobby) + 1];
	strcpy(hobby, C.hobby);
	weight = C.weight;
}

Cow::~Cow() { delete[] hobby; }

void Cow::ShowCow() const
{
	cout << name << endl;
	cout << hobby << endl;
	cout << weight << endl;
}

int main()
{
	Cow cow;
	Cow ccc("adads", "dsdfsad", 34);
	cow = ccc;
	cow.ShowCow();
	ccc.ShowCow();
}

习题2

#include 
#include 
#include 

using namespace std;

class String
{
	char* mp_text;
	unsigned m_text_length;
	void assignMember(const char* text)
	{
		m_text_length = strlen(text);
		mp_text = new char[m_text_length + 1];
		strcpy(mp_text, text);
	}
public:
	static const unsigned k_buffer_max_size = 256;
	const char* toCstr() const
	{
		return (mp_text);
	}
	String(const char* text = "")
	{
		assignMember(text);
	}
	String(const String& str)
	{
		assignMember(str.toCstr());
	}
	~String()
	{
		delete[] mp_text;
	}
	unsigned getLength() const
	{
		return (m_text_length);
	}
	void stringup()
	{
		for (unsigned i = 0; i < m_text_length; ++i)
			mp_text[i] = (char)toupper(mp_text[i]);
	}
	void stringlow()
	{
		for (unsigned i = 0; i < m_text_length; ++i)
			mp_text[i] = (char)tolower((int)mp_text[i]);
	}
	unsigned has(char ch) const
	{
		unsigned cnt = 0;
		for (unsigned i = 0; i < m_text_length; ++i)
			if (ch == mp_text[i])
				++cnt;
		return (cnt);
	}
	String& operator= (const String& str)
	{
		if (&str == this)
			return (*this);
		delete[] mp_text;
		assignMember(str.toCstr());
		return (*this);
	}
	String & operator+= (const String& str)
	{
		return (*this += str);
	}
	char& operator[] (unsigned idx)
	{
		return (mp_text[idx]);
	}
	const char & operator[] (unsigned idx) const
	{
		return (mp_text[idx]);
	}
	friend ostream & operator<< (ostream& os, const String& str)
	{
		os << str.toCstr();
		return (os);
	}
	friend istream & operator>> (istream& is, String& str)
	{
		char txt[k_buffer_max_size];
		if (is >> txt)
			str = txt;
		is.ignore(k_buffer_max_size, '\n');
		return (is);
	}
	friend bool operator< (const String& lvalue, const String& rvalue)
	{
		return (strcmp(lvalue.toCstr(), rvalue.toCstr()) < 0);
	}
	friend bool operator> (const String& lvalue, const String& rvalue)
	{
		return (rvalue < lvalue);
	}
	friend bool operator== (const String& lvalue, const String& rvalue)
	{
		return (!(lvalue < rvalue) && !(lvalue > rvalue));
	}
	friend bool operator<= (const String& lvalue, const String& rvalue)
	{
		return (!(lvalue > rvalue));
	}
	friend bool operator>= (const String& lvalue, const String& rvalue)
	{
		return (!(lvalue < rvalue));
	}
	friend String operator+ (const String& lvalue, const String& rvalue)
	{
		char* p_txt = new char[lvalue.getLength() + rvalue.getLength() + 1];
		strcpy(p_txt, lvalue.toCstr());
		strcat(p_txt, rvalue.toCstr());
		String tmp(p_txt);
		delete[] p_txt;
		return (tmp);
	}
};

int main()
{
	String s1(" and I am a C++ student.");
	String s2 = "Please enter your name: ";
	String s3;
	cout << s2;
	// overloaded << operator
	cin >> s3;
	// overloaded >> operator
	s2 = "My name is " + s3;
	// overloaded =, + operators
	cout << s2 << ".\n";
	s2 = s2 + s1;
	s2.stringup();
	// converts string to uppercase
	cout << "The string\n" << s2 << "\ncontains " << s2.has('A')
		<< " 'A' characters in it.\n";
	s1 = "red";
	// tstring(const char *),
	// then tstring & operator=(const string&)
	String rgb[3] = { String(s1), String("green"), String("blue") };
	cout << "enter the name of a primary color for mixing light: ";
	String ans;
	bool success = false;
	while (cin >> ans)
	{
		ans.stringlow();
		// converts string to lowercase
		for (int i = 0; i < 3; i++)
		{
			if (ans == rgb[i]) // overloaded == operator
			{
				cout << "That's right!\n";
				success = true;
				break;
			}
		}
		if (success)
			break;
		else
			cout << "Try again!\n";
	}
	cout << "Bye" << endl;
}

习题3

#include 
#include 

using namespace std;

class Stock
{
	char *company;
	int shares;
	double share_val;
	double total_val;
	void set_tot() { total_val = shares * share_val; };
public:
	Stock() {
		company = new char[8];
		strcpy(company, "no name");
		shares = 0;
		share_val = 0.0;
		total_val = 0.0;
	}
	Stock(const char *co, long n = 0, double pr = 0)
	{
		int len = strlen(co);
		company = new char[len + 1];
		strcpy(company, co);
		if (n < 0)
		{
			cout << "Number of shares can't be negative;"
				<< company << " shares set to 0" << endl;
			shares = 0;
		}
		else
			shares = n;
		share_val = pr;
		set_tot();
	}
	~Stock()
	{
		delete[]company;
	}
	void buy(long num, double price)
	{
		if (num < 0)
		{
			cout << "Number of shares purchase can't be negative."
				<< " Transaction is aborted." << endl;
		}
		else
		{
			shares += num;
			share_val = price;
			set_tot();
		}
	}
	void sell(long num, double price)
	{
		if (num < 0)
		{
			cout << "Number of shares sold can't be negative."
				<< "Transaction is aborted." << endl;
		}
		else if (num > shares)
		{
			cout << "You can't sell more than you have!"
				<< "Transaction is aborted." << endl;
		}
		else
		{
			shares -= num;
			share_val = price;
			set_tot();
		}
	}
	void update(double price)
	{
		share_val = price;
		set_tot();
	}
	const Stock &topval(const Stock &s)const
	{
		if (s.total_val > total_val)
			return s;
		else
			return *this;
	}
	friend ostream &operator<<(ostream &os, const Stock &s)
	{
		ios_base::fmtflags orig = os.setf(ios_base::fixed, ios_base::floatfield);
		streamsize prec = os.precision(3);
		os << "Company:" << s.company
			<< " Shares:" << s.shares << endl;
		os << " Share Price:$" << s.share_val;
		os.precision(2);
		os << " Total Worth:&" << s.total_val << endl;
		os.setf(orig, ios_base::floatfield);
		os.precision(prec);
		return os;
	}
};

const int STKS = 4;

int main()
{
	// create an array of initialized objects
	Stock stocks[STKS] = {
	Stock("NanoSmart", 12, 20.0),
	Stock("Boffo Objects", 200, 2.0),
	Stock("Monolithic Obelisks", 130, 3.25),
	Stock("Fleep Enterprises", 60, 6.5)
	};
	cout << "Stock holdings:\n";
	int st;
	for (st = 0; st < STKS; st++)
		cout << stocks[st];
	// set pointer to first element
	const Stock * top = &stocks[0];
	for (st = 1; st < STKS; st++)
		top = &top->topval(stocks[st]);
	// now top points to the most valuable holding
	cout << "\nMost valuable holding:\n";
	cout << *top;
	return 0;
}

习题4

#include 
using namespace std;
typedef unsigned long Item;

class Stack 
{
	enum { MAX = 10 };
	Item * items;
	int size;
	int top;
public:
	Stack(int n = MAX)
	{
		items = new Item[MAX];
		top = 0;
		size = 0;
	}
	Stack(const Stack &st)
	{
		items = new Item[st.size];
		top = 0;
		size = 0;
		for (int i = 0; i < st.size; i++)
		{
			items[i] = st.items[i];
			size++;
			top++;
		}
	}
	~Stack()
	{
		delete[] items;
	}
	bool isEmpty()
	{
		return top == 0;
	}
	bool isFull()
	{
		return top == MAX;
	}
	bool push(const Item &it)
	{
		if (isFull())
			cout << "error! Stack is full!" << endl;
		else
		{
			items[top++] = it;
			size++;
			return true;
		}
		return false;
	}
	bool pop(Item &item)
	{
		if (isEmpty())
			cout << "error! Stack is empty!" << endl;
		else
		{
			item = items[top--];
			size--;
			return true;
		}
		return false;
	}
	Stack & operator = (Stack &st)
	{
		delete[] items;
		items = new Item[st.size];
		top = 0;
		size = 0;
		for (int i = 0; i < st.size; i++)
		{
			items[i] = st.items[i];
			size++;
			top++;
		}
		return (*this);
	}
	friend ostream & operator<<(ostream &os, const Stack & st)
	{
		os << "This Stack is:" << endl;
		int len = st.top - 1;
		while (len != -1)
		{
			cout << st.items[len] << endl;
			len--;
		}
		return os;
	}
};


int main()
{
	Stack s;
	Item it[20] = { 0 };
	for (int i = 0; i < 11; i++)
	{
		it[i] = i + 1;
		s.push(it[i]);
	}
	cout << s;
	Stack s1(s);
	cout << "s1=" << s1;
	Stack s2 = s;
	cout << s;
}

习题5&6

// queue.h -- interface for a queue
#ifndef QUEUE_H_
#define QUEUE_H_
// This queue will contain Customer items
class Customer
{
private:
	long arrive; // arrival time for customer
	int processtime; // processing time for customer
public:
	Customer() : arrive(0), processtime(0) {}
	void set(long when);
	long when() const { return arrive; }
	int ptime() const { return processtime; }
};
typedef Customer Item;
class Queue
{
private:
	// class scope definitions
	// Node is a nested structure definition local to this class
	struct Node { Item item; struct Node * next; };
	enum { Q_SIZE = 10 };
	// private class members
	Node * front; // pointer to front of Queue
	Node * rear; // pointer to rear of Queue
	int items; // current number of items in Queue
	const int qsize; // maximum number of items in Queue
	// preemptive definitions to prevent public copying
	Queue(const Queue & q) : qsize(0) { }
	Queue & operator=(const Queue & q) { return *this; }
public:
	Queue(int qs = Q_SIZE); // create queue with a qs limit
	~Queue();
	bool isempty() const;
	bool isfull() const;
	int queuecount() const;
	bool enqueue(const Item &item); // add item to end
	bool dequeue(Item &item); // remove item from front
};
#endif



// queue.cpp -- Queue and Customer methods
#include "queue.h"
#include  // (or stdlib.h) for rand()
// Queue methods
Queue::Queue(int qs) : qsize(qs)
{
	front = rear = NULL;// or nullptr
	items = 0;
}
Queue::~Queue()
{
	Node * temp;
	while (front != NULL) // while queue is not yet empty
	{
		temp = front; // save address of front item
		front = front->next;// reset pointer to next item
		delete temp; // delete former front
	}
}
bool Queue::isempty() const
{
	return items == 0;
}
bool Queue::isfull() const
{
	return items == qsize;
}
int Queue::queuecount() const
{
	return items;
}
// Add item to queue
bool Queue::enqueue(const Item & item)
{
	if (isfull())
		return false;
	Node * add = new Node; // create node
	// on failure, new throws std::bad_alloc exception
	add->item = item; // set node pointers
	add->next = NULL; // or nullptr;
	items++;
	if (front == NULL) // if queue is empty,
		front = add; // place item at front
	else
		rear->next = add; // else place at rear
	rear = add; // have rear point to new node
	return true;
}
// Place front item into item variable and remove from queue
bool Queue::dequeue(Item & item)
{
	if (front == NULL)
		return false;
	item = front->item; // set item to first item in queue
	items--;
	Node * temp = front;// save location of first item
	front = front->next;// reset front to next item
	delete temp; // delete former first item
	if (items == 0)
		rear = NULL;
	return true;
}
// customer method
// when is the time at which the customer arrives
// the arrival time is set to when and the processing
// time set to a random value in the range 1 - 3
void Customer::set(long when)
{
	processtime = std::rand() % 3 + 1;
	arrive = when;
}



// bank.cpp -- using the Queue interface
// compile with queue.cpp
#include 
#include  // for rand() and srand()
#include  // for time()
#include "queue.h"
const int MIN_PER_HR = 60;
bool newcustomer(double x); // is there a new customer?
int main()
{
	using std::cin;
	using std::cout;
	using std::endl;
	using std::ios_base;
	// setting things up
	std::srand(std::time(0)); // random initializing of rand()
	cout << "Case Study: Bank of Heather Automatic Teller\n";
	cout << "Enter maximum size of queue: ";
	int qs;
	cin >> qs;
	Queue line(qs); // line queue holds up to qs people
	cout << "Enter the number of simulation hours: ";
	int hours; // hours of simulation
	cin >> hours;
	// simulation will run 1 cycle per minute
	long cyclelimit = MIN_PER_HR * hours; // # of cycles
	cout << "Enter the average number of customers per hour: ";
	double perhour; // average # of arrival per hour
	cin >> perhour;
	double min_per_cust;// average time between arrivals
	min_per_cust = MIN_PER_HR / perhour;
	Item temp; // new customer data
	long turnaways = 0; // turned away by full queue
	long customers = 0; // joined the queue
	long served = 0; // served during the simulation
	long sum_line = 0; // cumulative line length
	int wait_time = 0; // time until autoteller is free
	long line_wait = 0; // cumulative time in line
	// running the simulation
	for (int cycle = 0; cycle < cyclelimit; cycle++)
	{
		if (newcustomer(min_per_cust)) // have newcomer
		{
			if (line.isfull())
				turnaways++;
			else
			{
				customers++;
				temp.set(cycle); // cycle = time of arrival
				line.enqueue(temp); // add newcomer to line
			}
		}
		if (wait_time <= 0 && !line.isempty())
		{
			line.dequeue(temp); // attend next customer
			wait_time = temp.ptime(); // for wait_time minutes
			line_wait += cycle - temp.when();
			served++;
		}
		if (wait_time > 0)
			wait_time--;
		sum_line += line.queuecount();
	}
	// reporting results
	if (customers > 0)
	{
		cout << "customers accepted: " << customers << endl;
		cout << " customers served: " << served << endl;
		cout << " turnaways: " << turnaways << endl;
		cout << "average queue size: ";
		cout.precision(2);
		cout.setf(ios_base::fixed, ios_base::floatfield);
		cout << (double)sum_line / cyclelimit << endl;
		cout << " average wait time: "
			<< (double)line_wait / served << " minutes\n";
	}
	else
		cout << "No customers!\n";
	cout << "Done!\n";
	// cin.get();
	// cin.get();
	return 0;
}
// x = average time, in minutes, between customers
// return value is true if customer shows up this minute
bool newcustomer(double x)
{
	return (std::rand() * x / RAND_MAX < 1);
}