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C++ Primer Plus第十二章课后习题总结

article 2025/3/14 13:35:41

1. 对于下面的类声明：

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();
    Cow & operator=(const Cow & c);
    void ShowCow() const; // display all cow data
};

给这个类提供实现，并编写一个使用所有成员函数的小程序。

Cow.h:

#ifndef COW_H
#define COW_H
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();
    Cow & operator=(const Cow & c);
    void ShowCow() const; // display all cow data
};
#endif

Cow.cpp:

#include "Cow.h"
#include <iostream>
#include <cstring>
using namespace std;
Cow::Cow(){
	name[0] = '\0';
	hobby = nullptr;
	weight = 0.0;
}
Cow::Cow(const char * nm, const char * ho, double wt){
	strncpy(name, nm, 20);
	int len2 = strlen(ho);
	hobby = new char[len2 + 1];
	strcpy(hobby, ho);
	weight = wt;
}
Cow::Cow(const Cow &c){
	strncpy(name, c.name, 20);
	int len2 = strlen(c.hobby);
	hobby = new char[len2 + 1];
	strcpy(hobby, c.hobby);
	weight = c.weight;
}
Cow::~Cow(){
	delete[] hobby;
}
Cow & Cow::operator=(const Cow & c){
	if(this == &c)
		return *this;
	strncpy(name, c.name, 20);
	delete[] hobby;
	int len2 = strlen(c.hobby);
	hobby = new char[len2 + 1];
	strcpy(hobby, c.hobby);
	weight = c.weight;
	return *this;
}
void Cow::ShowCow() const{
	cout << "name:" << name;
	cout << endl;
	cout << "hobby:" << hobby;
	cout << endl;
	cout << "weight:" << weight;
	cout << endl;
	cout << endl;
}

main.cpp:

#include "Cow.h"
#include <iostream>

/* run this program using the console pauser or add your own getch, system("pause") or input loop */

int main(int argc, char** argv) {
	//c1调用构造函数Cow(const char * nm, const char * ho, double wt); 
	Cow c1("xiaoyu", "eating", 100);
  	c1.ShowCow();
  	//c2调用复制构造函数Cow(const Cow &c); 
  	Cow c2 = c1;
  	c2.ShowCow();
  	//c3调用赋值运算符重载函数Cow & operator=(const Cow & c); 
  	Cow c3;
  	c3 = c2;
  	c3.ShowCow();
	return 0;
}

运行结果：

 2. 通过下面的工作来改进String类声明（即将String1.h升级为String2.h）。

a. 对+运算符进行重载，使之可将两个字符串合并成一个。

b. 提供一个Stringlow()成员函数，将字符串中所有的字母字符转换为小写（别忘了cctype系列字符函数）。

c. 提供String()成员函数，将字符串中所有字母字符转换成大写。

d. 提供一个这样的成员函数，它接受一个char参数，返回该字符在字符串中出现的次数。

使用下面的程序来测试您的工作：

// pe12_2.cpp
#include <iostream>
using namespace std;
#include "string2.h"
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"; // String(const char *),
    // then String & 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\n";
    return 0;
}

输出应与下面相似：

Please enter your name: Fretta Farbo
My name is Fretta Farbo.
The string
MY NAME IS FRETTA FARBO AND I AM A C++ STUDENT.
contains 6 'A' characters in it.
Enter the name of a primary color for mixing light: yellow
Try again!
BLUE
That's right!
Bye

String.h:

#ifndef STRING_H
#define STRING_H

#include <iostream>
using std::ostream;
using std::istream;
class String{
	private:
		char *str;
		int len;
		//static int num_strings;
		
	public:
		static const int CINLIM = 80;
		//constructors and other methods
		String();
		String(const char*);
		String(const String &);
		~String();
		int length()const{return len;}
		void stringlow();
		void stringup();
		int has(char c)const;
		//overload operator methods
		String operator+(String &);
//		String operator+(const char *s) const;
		String &operator=(const String &);
		String &operator=(const char *);
		char &operator[](int);
		const char &operator[](int)const;
		//overload operator friends
		//friend bool operator<(const String &, const String &);
		//friend bool operator>(const String &, const String &);
		friend bool operator==(const String &, const String &);
		friend String operator+(const char *, String &);
		friend ostream &operator<<(ostream &, const String &);
		friend istream &operator>>(istream &, String &);
		//static function
		//static int HowMany();
};
#endif

String.cpp:

#include "String.h"
#include <cstring>
#include  <cctype>

//constructors and other methods
String::String(){
	str = new char[1];
	str[0] = '\0';
	len = 0;
}
String::String(const char* s){
	len = strlen(s);
	str = new char[len + 1];
	strcpy(str, s);
}
String::String(const String &s){
	len = s.len;
	str = new char[len + 1];
	strcpy(str, s.str);
}
String::~String(){
	delete[] str;
}
void String::stringlow(){
	for(int i = 0; i < len; i++){
		str[i] = tolower(str[i]);
	}
} 
void String::stringup(){
	for(int i = 0; i < len; i++){
		str[i] = toupper(str[i]);
	}
} 
int String::has(char c)const{
	int ch = 0;
	for(int i = 0; i < len; i++){
		if(str[i] == '\n'){
			break;
		}
		if(str[i] == 'c'){
			ch++;
		}
	}
	return ch;
}

//overload operator methods
String String::operator+(String &s){
	int lengt = len + s.len;
	char *temp = new char[lengt + 1];
	strcpy(temp, str);
	strcat(temp, s.str);
	String result = temp;//调用构造函数 
	delete[] temp;
	return result;
}
//String String::operator+(const char *s) const {
//	String tmp = s;
//	String sum = *this + tmp;
//	return sum;
//}
String &String::operator=(const String &st){
	if(this == &st)
		return *this;
	delete[] str;
	len = strlen(st.str);
	str = new char[len + 1];
	strcpy(str, st.str);
	return *this;
}
String &String::operator=(const char *s){
	delete[] str;
	len = strlen(s);
	str = new char[len + 1];
	strcpy(str, s);
	return *this;
}
char &String::operator[](int i){
	return str[i];
}
const char &String::operator[](int i)const{
	return str[i];
}

//overload operator friends
bool operator==(const String &str1, const String &str2){
	return (strcmp(str1.str, str2.str) == 0);
}
ostream &operator<<(ostream & os, const String & st){
	os << st.str;
	return os;
}
istream &operator>>(istream & is, String & st){
	char temp[String::CINLIM];
	is.get(temp, String::CINLIM);
	if(is)
		st = temp;//使用了赋值运算符重载函数 
	while(is && is.get() != '\n')
		continue;
	return is;
}
String operator+(const char *s, String &ss){
	return String(s) + ss;
}

main.cpp: 

#include "String.h"
#include <iostream>
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */

int main(int argc, char** argv) {
	String s1(" and I am a C++ student.");//constructor 
    String s2 = "Please enter your name: ";//overloaded = operator
    String s3;
    cout << s2; // overloaded << operator
    cin >> s3; // overloaded >> operator
    s2 = "My name is " + s3; // overloaded =, + operators(friend)
    cout << s2 << ".\n";// overloaded << operator
    s2 = s2 + s1;// overloaded =, + operators
    s2.stringup(); // converts string to uppercase
    cout << "The string\n" << s2 << "\ncontains " << s2.has('A')
        << " 'A' characters in it.\n";// overloaded << operator
    s1 = "red"; // String(const char *),
    // then String 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\n";
	return 0;
}

输出结果如下： 

 3. 新编写程序清单10.7和程序清单10.8描述的Stock类，使之使用动态分配的内存，而不是string类对象来存储股票名称。另外，使用重载的operator<<()定义代替show()成员函数。再使用程序清单10.9测试新的定义程序。

Stock.h:

#ifndef STOCK_H
#define STOCK_H
#include <iostream>
using namespace std; 
class Stock{
	private:
		char *company;
		int shares;
		double share_val;
  		double total_val;
  		void set_tot() { total_val = shares * share_val; }
  	public:
  		Stock();  // default constructor
  		Stock(const char * co, long n, double pr);
  		~Stock();  // do-nothing destructor
  		void buy(long num, double price);
  		void sell(long num, double price);
  		void update(double price);
  		friend ostream& operator<<(ostream& os, const Stock& st);
  		const Stock& topval(const Stock& s) const;
};
#endif

Stock.cpp:

#include "stock.h"
#include <cstring>
#include <iostream>
using namespace std;
Stock::Stock() {
	company = new char[8];
	strcpy(company, "no name");
	shares = 0;
	share_val = 0.0;
	total_val = 0.0;
}
Stock::Stock(const char * co, long n, double pr) {
	company = new char[strlen(co) + 1];
	strcpy(company, co);
	if(n < 0) {
		cout << "Number of shares can't be negative;"
		     << company << "shares set to 0.\n";
		shares =0;
	} else
		shares = n;
	share_val = pr;
	set_tot();
}
Stock::~Stock(){
	delete[] company;
}
void Stock::buy(long num, double price) {
	if (num < 0) {
		cout << "Number of shares purchased can’t be negative. "
		     << "Transaction is aborted.\n";
	} else {
		shares += num;
		share_val = price;
		set_tot();
	}
}
void Stock::sell(long num, double price) {
	if (num < 0) {
		cout << "Number of shares sold can’t be negative. "
		     << "Transaction is aborted.\n";
	} else if (num > shares) {
		cout << "You can’t sell more than you have! "
		     << "Transaction is aborted.\n";
	} else {
		shares -= num;
		share_val = price;
		set_tot();
	}
}
void Stock::update(double price) {
	share_val = price;
	set_tot();
}
ostream& operator<<(ostream& os, const Stock& st) {
	ios_base::fmtflags orig = os.setf(ios_base::fixed, ios_base::floatfield);
	std::streamsize prec = os.precision(3);
	os << "Company: " << st.company << " Shares: " << st.shares << '\n';
	os << " Share Price: $" << st.share_val;
	// set format to #.##
	os.precision(2);
	os << " Total Worth: $" << st.total_val << '\n';
	// restore original format
	os.setf(orig, ios_base::floatfield);
	os.precision(prec);
	return os;
}
const Stock& Stock::topval(const Stock& s) const {
	if (s.total_val > total_val)
		return s;
	else
		return *this;
}

main.cpp:

#include <iostream>
#include "stock.h"
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
const int STKS = 4;
int main(int argc, char** argv) {
	Stock stocks[STKS] = {
		Stock("NanoSmart", 12, 20.0),
		Stock("Boffo objects", 200, 2.0),
		Stock("Monolithic belisks", 130, 3.25),
		Stock("Fleep Enterprises", 60, 6.5),
	};
	cout << "Stock holdings:\n";
	int st;
	for(st = 0; st < STKS; st++){
		cout << stocks[st];
	}
	const Stock *top = &stocks[0];
	for(st = 1; st < STKS; st++){
		top = &top->topval(stocks[st]);
	}
	cout << "\nMost valuable holding:\n";
	cout << *top;
	return 0;
}

输出结果：

 4.请看下面程序清单10.10定义的Stack类的变量：

// stack.h -- class declaration for the stack ADT
typedef unsigned long Item;
class Stack
{
    private:
    enum {MAX = 10}; // constant specific to class
    Item * pitems; // holds stack items
    int size; // number of elements in stack
    int top; // index for top stack item
    public:
    Stack(int n = MAX); // creates stack with n elements
    Stack(const Stack & st);
    ~Stack();
    bool isempty() const;
    bool isfull() const;
    // push() returns false if stack already is full, true otherwise
    bool push(const Item & item); // add item to stack
    // pop() returns false if stack already is empty, true otherwise
    bool pop(Item & item); // pop top into item
    Stack & operator=(const Stack & st);
};

正如私有成员表明的，这个类使用动态分配的数组来保存栈项。请重新编写方法，以适应这种新的表示法，并编写一个程序来演示所有的方法，包括复制构造函数和赋值运算符。

Stack.h:

#ifndef STACK_H
#define STACK_H
#include <iostream>
using namespace std;
typedef unsigned long Item;
class Stack {
	private:
		enum {MAX = 10}; // constant specific to class
		Item * pitems; // holds stack items
		int size; // number of elements in stack
		int top; // index for top stack item
	public:
		Stack(int n = MAX); // creates stack with n elements
		Stack(Item* it, int s, int t);
		Stack(const Stack & st);
		~Stack();
		bool isempty() const;
		bool isfull() const;
		// push() returns false if stack already is full, true otherwise
		bool push(const Item & item); // add item to stack
		// pop() returns false if stack already is empty, true otherwise
		bool pop(Item & item); // pop top into item
		Stack & operator=(const Stack & st);
		friend ostream &operator<<(ostream &, const Stack &);
};
#endif

Stack.cpp:

#include "Stack.h"
Stack::Stack(int n){
	size = MAX;
	top = 0;
	pitems = new Item[size];
	for(int i = 0; i < size; i++)
		pitems[i] = 0;
}
Stack::Stack(Item* it, int s, int t){
	size = s;
	top = t;
	pitems = new Item[s];
	for(int i = 0; i < size; i++)
		pitems[i] = it[i];
}
Stack::Stack(const Stack & st){
	size = st.size;
	top = st.top;
	pitems = new Item[size];
	for(int i = 0; i < size; i++)
		pitems[i] = st.pitems[i];
}
Stack::~Stack(){
	delete[] pitems;
	size = 0;
	top = 0;
} 
bool Stack::isempty() const{
	if(top == 0)
		return true;
	else
		return false;
}
bool Stack::isfull() const{
	if(top == MAX)
		return true;
	else
		return false;
}
bool Stack::push(const Item & item){
	if(this->Stack::isfull())
		return false;
	size += 1;
	top++;
	pitems[top] = item;
}
bool Stack::pop(Item & item){
	if(this->isempty())
		return false;
	size -= 1;
	item = pitems[top];
	top--;
}
Stack & Stack::operator=(const Stack & st){
	if(this == &st)
		return *this;
	size = st.size;
	top = st.top;
	delete[] pitems;
	pitems = new Item[size];
	for(int i = 0; i < size; i++)
		pitems[i] = st.pitems[i];
	return *this;
}
ostream &operator<<(ostream &os, const Stack &s){
	for(int i = 0; i < s.size; i++)
		os << s.pitems[i] << endl;
	return os;
}

main.cpp:

#include <iostream>
#include <cctype>
#include "Stack.h"
using namespace std;
/* run this program using the console pauser or add your own getch, system("pause") or input loop */

int main(int argc, char** argv) {
	Stack st;  // create an empty stack
	char ch;
	unsigned long po;
	cout << "Please enter A to add a purchase order,\n"
	     << "P to process a PO, or Q to quit.\n";
	while (cin >> ch && toupper(ch) != 'Q') {
		while (cin.get() != '\n') continue;
		if (!isalpha(ch)) {
			cout << '\a';
			continue;
		}
		switch (ch) {
			case 'A':
			case 'a':
				cout << "Enter a PO number to add: ";
				cin >> po;
				if (st.isfull())
					cout << "stack already full\n";
				else
					st.push(po);
				break;
			case 'P':
			case 'p':
				if (st.isempty())
					cout << "stack already empty\n";
				else {
					st.pop(po);
					cout << "PO #" << po << " popped\n";
				}
				break;
		}
		cout << "Please enter A to add a purchase order,\n"
		     << "P to process a PO, or Q to quit.\n";
	}
	Stack st2;
	st2 = st;
	cout << "stack2 = stack is:\n" << st2;

	cout << "Bye\n";
	return 0;
}

输出如下： 


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