第十二章编程练习答案

12.1根据以下类声明，完成类，并编小程序使用它

//12.1根据以下类声明，完成类，并编小程序使用它
#include <iostream>
#include <cstring>
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();
}

12.2根据以下的主函数，编写类，使得：
a.重载+，使得两个字符串可以合并为一个
b.使用Stringlow()成员函数，使得字母可以转换为小写
c.使用Stringup()成员函数，使得字母可转换为大写
d.提供一个成员函数，使它返回一个char字符出现的个数

//12.2根据以下的主函数，编写类，使得：
//a.重载+，使得两个字符串可以合并为一个
//b.使用Stringlow()成员函数，使得字母可以转换为小写
//c.使用Stringup()成员函数，使得字母可转换为大写
//d.提供一个成员函数，使它返回一个char字符出现的个数
#include <iostream>
#include <cstring>
#include <cctype>
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;
}

12.3重新编写程序清单10.7,10.8，使用动态内存并重载<<代替show()

//12.3重新编写程序清单10.7,10.8，使用动态内存并重载<<代替show()
#include <iostream>
#include <cstring>
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; 
}

12.4按以下类声明，完成类，并编写一个演示程序

//12.4按以下类声明，完成类，并编写一个演示程序
#include <iostream>
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;
}

12.5-12.6银行ATM顾客系统

// 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 <cstdlib>         // (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 <iostream>
#include <cstdlib> // for rand() and srand()
#include <ctime>   // 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); 
}

c++ primer plus(第6版)中文版 第十二章编程练习答案,布布扣,bubuko.com

c++ primer plus(第6版)中文版 第十二章编程练习答案