C++ primer Plus（第六版）中文版 第十二章 类和动态内存分配 编程练习答案
2019-01-20 19:41
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第十二章 类和动态内存分配
1. 对于下面的声明：
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函数成员的小程序。
cow.h
[code]//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
[code]//cow.cpp
#include <iostream>
#include <cstring>
#include "cow.h"
using namespace std;
Cow::Cow()
{
strcpy(name, "None");
hobby = new char[1];
hobby[0] = '\0';
weight = 0.0;
}
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;
}
Cow & Cow::operator=(const Cow & c)
{
if (this == &c)
return *this;
strcpy(name, c.name);
delete [] hobby;
hobby = new char[strlen(c.hobby)+1];
strcpy(hobby, c.hobby);
weight = c.weight;
return *this;
}
void Cow::ShowCow() const
{
cout << "Name：\t" << name << endl;
cout << "Hobby：\t" << hobby << endl;
cout << "Weight：\t" << weight << endl;
cout << endl;
}
//usecow.cpp
[code]//usecow.cpp
#include <iostream>
#include <cstring>
#include "cow.h"
using namespace std;
int main()
{
Cow one; //使用默认构造函数
Cow two("Lucy", "吃草", 125.25); //使用构造函数
one.ShowCow();
two.ShowCow();
one = two; //使用重载赋值运算符
Cow three(one); //使用复制构造函数
Cow four = one; //使用复制构造函数
one.ShowCow();
three.ShowCow();
four.ShowCow();
return 0;
}
2. 通过完成下面的工作来改进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1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Stringup()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：
[code]// 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
string1如下：
[code]//string1.h
// string1.h -- fixed and augmented string class definition
#ifndef STRING1_H_
#define STRING1_H_
#include <iostream>
using std::ostream;
using std::istream;
class String
{
private:
char * str; // pointer to string
int len; // length of string
static int num_strings; // number of objects
static const int CINLIM = 80; // cin input limit
public:
// constructors and other methods
String(const char * s); // constructor
String(); // default constructor
String(const String &); // copy constructor
~String(); // destructor
int length () const { return len; }
// overloaded operator methods
String & operator=(const String &);
String & operator=(const char *);
char & operator[](int i);
const char & operator[](int i) const;
// overloaded operator friends
friend bool operator<(const String &st, const String &st2);
friend bool operator>(const String &st1, const String &st2);
friend bool operator==(const String &st, const String &st2);
friend ostream & operator<<(ostream & os, const String & st);
friend istream & operator>>(istream & is, String & st);
// static function
static int HowMany();
};
#endif
[code]//string1.cpp
// string1.cpp -- String class methods
#include <cstring> // string.h for some
#include "string1.h" // includes <iostream>
using std::cin;
using std::cout;
// initializing static class member
int String::num_strings = 0;
// static method
int String::HowMany()
{
return num_strings;
}
// class methods
String::String(const char * s) // construct String from C string
{
len = std::strlen(s); // set size
str = new char[len + 1]; // allot storage
std::strcpy(str, s); // initialize pointer
num_strings++; // set object count
}
String::String() // default constructor
{
len = 4;
str = new char[1];
str[0] = '\0'; // default string
num_strings++;
}
String::String(const String & st)
{
num_strings++; // handle static member update
len = st.len; // same length
str = new char [len + 1]; // allot space
std::strcpy(str, st.str); // copy string to new location
}
String::~String() // necessary destructor
{
--num_strings; // required
delete [] str; // required
}
// overloaded operator methods
// assign a String to a String
String & String::operator=(const String & st)
{
if (this == &st)
return *this;
delete [] str;
len = st.len;
str = new char[len + 1];
std::strcpy(str, st.str);
return *this;
}
// assign a C string to a String
String & String::operator=(const char * s)
{
delete [] str;
len = std::strlen(s);
str = new char[len + 1];
std::strcpy(str, s);
return *this;
}
// read-write char access for non-const String
char & String::operator[](int i)
{
return str[i];
}
// read-only char access for const String
const char & String::operator[](int i) const
{
return str[i];
}
// overloaded operator friends
bool operator<(const String &st1, const String &st2)
{
return (std::strcmp(st1.str, st2.str) < 0);
}
bool operator>(const String &st1, const String &st2)
{
return st2 < st1;
}
bool operator==(const String &st1, const String &st2)
{
return (std::strcmp(st1.str, st2.str) == 0);
}
// simple String output
ostream & operator<<(ostream & os, const String & st)
{
os << st.str;
return os;
}
// quick and dirty String input
istream & operator>>(istream & is, String & st)
{
char temp[String::CINLIM];
is.get(temp, String::CINLIM);
if (is)
st = temp;
while (is && is.get() != '\n')
continue;
return is;
}
2.1 修改后的string2.h
[code]#ifndef STRING2_H_
#define STRING2_H_
#include <iostream>
using std::ostream;
using std::istream;
class String
{
private:
char * str; // pointer to string
int len; // length of string
static int num_strings; // number of objects
static const int CINLIM = 80; // cin input limit
public:
// constructors and other methods
String(const char * s); // constructor
String(); // default constructor
String(const String &); // copy constructor
~String(); // destructor
int length () const { return len; }
void stringlow(); //成员函数，转换为小写
void stringup(); //成员函数，转换为大写
int has(const char); //成员函数，统计字符次数
// overloaded operator methods
String & operator=(const String &);
String & operator=(const char *);
char & operator[](int i);
const char & operator[](int i) const;
// overloaded operator friends
friend String operator+(const String &st1, const String &st2); //重载+运算符
friend bool operator<(const String &st, const String &st2);
friend bool operator>(const String &st1, const String &st2);
friend bool operator==(const String &st, const String &st2);
friend ostream & operator<<(ostream & os, const String & st);
friend istream & operator>>(istream & is, String & st);
// static function
static int HowMany();
};
#endif
[code]//string2.cpp
// string2.cpp -- String class methods
#include <cstring> // string.h for some
#include <cctype>
#include "string2.h" // includes <iostream>
using std::cin;
using std::cout;
// initializing static class member
int String::num_strings = 0;
// static method
int String::HowMany()
{
return num_strings;
}
// class methods
String::String(const char * s) // construct String from C string
{
len = std::strlen(s); // set size
str = new char[len + 1]; // allot storage
std::strcpy(str, s); // initialize pointer
num_strings++; // set object count
}
String::String() // default constructor
{
len = 4;
str = new char[1];
str[0] = '\0'; // default string
num_strings++;
}
String::String(const String & st)
{
num_strings++; // handle static member update
len = st.len; // same length
str = new char [len + 1]; // allot space
std::strcpy(str, st.str); // copy string to new location
}
String::~String() // necessary destructor
{
--num_strings; // required
delete [] str; // required
}
// overloaded operator methods
// assign a String to a String
String & String::operator=(const String & st)
{
if (this == &st)
return *this;
delete [] str;
len = st.len;
str = new char[len + 1];
std::strcpy(str, st.str);
return *this;
}
// assign a C string to a String
String & String::operator=(const char * s)
{
delete [] str;
len = std::strlen(s);
str = new char[len + 1];
std::strcpy(str, s);
return *this;
}
// read-write char access for non-const String
char & String::operator[](int i)
{
return str[i];
}
// read-only char access for const String
const char & String::operator[](int i) const
{
return str[i];
}
// overloaded operator friends
bool operator<(const String &st1, const String &st2)
{
return (std::strcmp(st1.str, st2.str) < 0);
}
bool operator>(const String &st1, const String &st2)
{
return st2 < st1;
}
bool operator==(const String &st1, const String &st2)
{
return (std::strcmp(st1.str, st2.str) == 0);
}
// simple String output
ostream & operator<<(ostream & os, const String & st)
{
os << st.str;
return os;
}
// quick and dirty String input
istream & operator>>(istream & is, String & st)
{
char temp[String::CINLIM];
is.get(temp, String::CINLIM);
if (is)
st = temp;
while (is && is.get() != '\n')
continue;
return is;
}
void String::stringlow() //成员函数，转换为小写
{
for (int i = 0; i < len; i++)
str[i] = tolower(str[i]);
}
void String::stringup() //成员函数，转换为大写
{
for (int i = 0; i < len; i++)
str[i] = toupper(str[i]);
}
int String::has(const char a) //成员函数，统计字符次数
{
int num = 0;
for (int i = 0; i < len; i++)
{
if(str[i] == a)
num++;
}
return num;
}
String operator+(const String &st1, const String &st2)
{
String add;
add.len = st1.len + st2.len;
add.str = new char[add.len + 1];
strcpy(add.str, st1.str);
strcat(add.str, st2.str);
return add;
}
2.2 或者 修改后的string2.h
[code]#ifndef STRING2_H_
#define STRING2_H_
#include <iostream>
using std::ostream;
using std::istream;
class String
{
private:
char * str; // pointer to string
int len; // length of string
static int num_strings; // number of objects
static const int CINLIM = 80; // cin input limit
public:
// constructors and other methods
String(const char * s); // constructor
String(); // default constructor
String(const String &); // copy constructor
~String(); // destructor
int length () const { return len; }
void stringlow(); //成员函数，转换为小写
void stringup(); //成员函数，转换为大写
int has(const char); //成员函数，统计字符次数
// overloaded operator methods
String & operator=(const String &);
String & operator=(const char *);
char & operator[](int i);
const char & operator[](int i) const;
// overloaded operator friends
friend String operator+(const String &st1, const String &st2); //重载+运算符 String + String
friend String operator+(const char * s, const String &st); //重载+运算符 C字符串 + String
friend String operator+(const String &st, const char * s) {return (s + st);} //重载+运算符 String + C字符串
friend bool operator<(const String &st, const String &st2);
friend bool operator>(const String &st1, const String &st2);
friend bool operator==(const String &st, const String &st2);
friend ostream & operator<<(ostream & os, const String & st);
friend istream & operator>>(istream & is, String & st);
// static function
static int HowMany();
};
#endif
[code]//string2.cpp
// string2.cpp -- String class methods
#include <cstring> // string.h for some
#include <cctype>
#include "string2.h" // includes <iostream>
using std::cin;
using std::cout;
// initializing static class member
int String::num_strings = 0;
// static method
int String::HowMany()
{
return num_strings;
}
// class methods
String::String(const char * s) // construct String from C string
{
len = std::strlen(s); // set size
str = new char[len + 1]; // allot storage
std::strcpy(str, s); // initialize pointer
num_strings++; // set object count
}
String::String() // default constructor
{
len = 4;
str = new char[1];
str[0] = '\0'; // default string
num_strings++;
}
String::String(const String & st)
{
num_strings++; // handle static member update
len = st.len; // same length
str = new char [len + 1]; // allot space
std::strcpy(str, st.str); // copy string to new location
}
String::~String() // necessary destructor
{
--num_strings; // required
delete [] str; // required
}
// overloaded operator methods
// assign a String to a String
String & String::operator=(const String & st)
{
if (this == &st)
return *this;
delete [] str;
len = st.len;
str = new char[len + 1];
std::strcpy(str, st.str);
return *this;
}
// assign a C string to a String
String & String::operator=(const char * s)
{
delete [] str;
len = std::strlen(s);
str = new char[len + 1];
std::strcpy(str, s);
return *this;
}
// read-write char access for non-const String
char & String::operator[](int i)
{
return str[i];
}
// read-only char access for const String
const char & String::operator[](int i) const
{
return str[i];
}
// overloaded operator friends
bool operator<(const String &st1, const String &st2)
{
return (std::strcmp(st1.str, st2.str) < 0);
}
bool operator>(const String &st1, const String &st2)
{
return st2 < st1;
}
bool operator==(const String &st1, const String &st2)
{
return (std::strcmp(st1.str, st2.str) == 0);
}
// simple String output
ostream & operator<<(ostream & os, const String & st)
{
os << st.str;
return os;
}
// quick and dirty String input
istream & operator>>(istream & is, String & st)
{
char temp[String::CINLIM];
is.get(temp, String::CINLIM);
if (is)
st = temp;
while (is && is.get() != '\n')
continue;
return is;
}
void String::stringlow() //成员函数，转换为小写
{
for (int i = 0; i < len; i++)
str[i] = tolower(str[i]);
}
void String::stringup() //成员函数，转换为大写
{
for (int i = 0; i < len; i++)
str[i] = toupper(str[i]);
}
int String::has(const char a) //成员函数，统计字符次数
{
int num = 0;
for (int i = 0; i < len; i++)
{
if(str[i] == a)
num++;
}
return num;
}
String operator+(const String &st1, const String &st2)
{
String add;
add.len = st1.len + st2.len;
add.str = new char[add.len + 1];
strcpy(add.str, st1.str);
strcat(add.str, st2.str);
return add;
}
String operator+(const char * s, const String &st)
{
String add;
add.len = std::strlen(s) + st.len;
add.str = new char[add.len + 1];
strcpy(add.str, s);
strcat(add.str, st.str);
return add;
}
2.3 再或者
[code]#ifndef STRING2_H_
#define STRING2_H_
#include <iostream>
using std::ostream;
using std::istream;
class String
{
private:
char * str; // pointer to string
int len; // length of string
static int num_strings; // number of objects
static const int CINLIM = 80; // cin input limit
public:
// constructors and other methods
String(const char * s); // constructor
String(); // default constructor
String(const String &); // copy constructor
~String(); // destructor
int length() const { return len; }
void stringlow(); //成员函数，转换为小写
void stringup(); //成员函数，转换为大写
int has(const char); //成员函数，统计字符次数
// overloaded operator methods
String & operator=(const String &);
String & operator=(const char *);
char & operator[](int i);
const char & operator[](int i) const;
String operator+(const String &st) const; //重载+运算符 String + String
String operator+(const char * s) const; //重载+运算符 C字符串 + String
// overloaded operator friends
friend String operator+(const char * s, const String &st) { return (st + s); } //重载+运算符 String + C字符串
friend bool operator<(const String &st, const String &st2);
friend bool operator>(const String &st1, const String &st2);
friend bool operator==(const String &st, const String &st2);
friend ostream & operator<<(ostream & os, const String & st);
friend istream & operator>>(istream & is, String & st);
// static function
static int HowMany();
};
#endif
[code]//string2.cpp
#include <cstring> // string.h for some
#include <cctype>
#include "string2.h" // includes <iostream>
using std::cin;
using std::cout;
// initializing static class member
int String::num_strings = 0;
// static method
int String::HowMany()
{
return num_strings;
}
// class methods
String::String(const char * s) // construct String from C string
{
len = std::strlen(s); // set size
str = new char[len + 1]; // allot storage
std::strcpy(str, s); // initialize pointer
num_strings++; // set object count
}
String::String() // default constructor
{
len = 4;
str = new char[1];
str[0] = '\0'; // default string
num_strings++;
}
String::String(const String & st)
{
num_strings++; // handle static member update
len = st.len; // same length
str = new char[len + 1]; // allot space
std::strcpy(str, st.str); // copy string to new location
}
String::~String() // necessary destructor
{
--num_strings; // required
delete[] str; // required
}
// overloaded operator methods
// assign a String to a String
String & String::operator=(const String & st)
{
if (this == &st)
return *this;
delete[] str;
len = st.len;
str = new char[len + 1];
std::strcpy(str, st.str);
return *this;
}
// assign a C string to a String
String & String::operator=(const char * s)
{
delete[] str;
len = std::strlen(s);
str = new char[len + 1];
std::strcpy(str, s);
return *this;
}
// read-write char access for non-const String
char & String::operator[](int i)
{
return str[i];
}
// read-only char access for const String
const char & String::operator[](int i) const
{
return str[i];
}
// overloaded operator friends
bool operator<(const String &st1, const String &st2)
{
return (std::strcmp(st1.str, st2.str) < 0);
}
bool operator>(const String &st1, const String &st2)
{
return st2 < st1;
}
bool operator==(const String &st1, const String &st2)
{
return (std::strcmp(st1.str, st2.str) == 0);
}
// simple String output
ostream & operator<<(ostream & os, const String & st)
{
os << st.str;
return os;
}
// quick and dirty String input
istream & operator>>(istream & is, String & st)
{
char temp[String::CINLIM];
is.get(temp, String::CINLIM);
if (is)
st = temp;
while (is && is.get() != '\n')
continue;
return is;
}
void String::stringlow() //成员函数，转换为小写
{
for (int i = 0; i < len; i++)
str[i] = tolower(str[i]);
}
void String::stringup() //成员函数，转换为大写
{
for (int i = 0; i < len; i++)
str[i] = toupper(str[i]);
}
int String::has(const char a) //成员函数，统计字符次数
{
int num = 0;
for (int i = 0; i < len; i++)
{
if (str[i] == a)
num++;
}
return num;
}
String String::operator+(const String &st) const
{
String add;
add.len = len + st.len;
add.str = new char[add.len + 1];
strcpy(add.str, str);
strcat(add.str, st.str);
return add;
}
String String::operator+(const char * s) const
{
String add;
add.len = std::strlen(s) + len;
add.str = new char[add.len + 1];
strcpy(add.str, s);
strcat(add.str, str);
return add;
}
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show()成员函数。再使用程序清单10.9 测试新的定义程序。
程序清单10.7
[code]// stock20.h -- augmented version
#ifndef STOCK20_H_
#define STOCK20_H_
#include <string>
class Stock
{
private:
std::string company;
int shares;
double share_val;
double total_val;
void set_tot() { total_val = shares * share_val; }
public:
Stock(); // default constructor
Stock(const std::string & co, long n = 0, double pr = 0.0);
~Stock(); // do-nothing destructor
void buy(long num, double price);
void sell(long num, double price);
void update(double price);
void show()const;
const Stock & topval(const Stock & s) const;
};
#endif
程序清单10.8
[code]// stock20.cpp -- augmented version
#include <iostream>
#include "stock20.h"
using namespace std;
// constructors
Stock::Stock() // default constructor
{
company = "no name";
shares = 0;
share_val = 0.0;
total_val = 0.0;
}
Stock::Stock(const std::string & co, long n, double pr)
{
company = co;
if (n < 0)
{
std::cout << "Number of shares can't be negative; "
<< company << " shares set to 0.\n";
shares = 0;
}
else
shares = n;
share_val = pr;
set_tot();
}
// class destructor
Stock::~Stock() // quiet class destructor
{
}
// other methods
void Stock::buy(long num, double price)
{
if (num < 0)
{
std::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)
{
using std::cout;
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();
}
void Stock::show() const
{
using std::cout;
using std::ios_base;
// set format to #.###
ios_base::fmtflags orig =
cout.setf(ios_base::fixed, ios_base::floatfield);
std::streamsize prec = cout.precision(3);
cout << "Company: " << company
<< " Shares: " << shares << '\n';
cout << " Share Price: $" << share_val;
// set format to #.##
cout.precision(2);
cout << " Total Worth: $" << total_val << '\n';
// restore original format
cout.setf(orig, ios_base::floatfield);
cout.precision(prec);
}
const Stock & Stock::topval(const Stock & s) const
{
if (s.total_val > total_val)
return s;
else
return *this;
}
程序清单10.9
[code]// usestok2.cpp -- using the Stock class
// compile with stock20.cpp
#include <iostream>
#include "stock20.h"
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)
};
std::cout << "Stock holdings:\n";
int st;
for (st = 0; st < STKS; st++)
stocks[st].show();
// 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
std::cout << "\nMost valuable holding:\n";
top->show();}
// std::cin.get();
return 0;
}
修改后 程序清单10.7
[code]// stock20.h -- augmented version
#ifndef STOCK20_H_
#define STOCK20_H_
class Stock
{
private:
char * company; //改为char *
int shares;
double share_val;
double total_val;
void set_tot() { total_val = shares * share_val; }
public:
Stock(); //默认构造函数
Stock(const char * co, long n = 0, double pr = 0.0); //构造函数
Stock(const Stock &); //复制构造函数
~Stock(); // 析构函数
void buy(long num, double price);
void sell(long num, double price);
void update(double price);
// void show()const;
const Stock & topval(const Stock & s) const;
Stock & operator=(const Stock &); //重载赋值运算符
friend ostream & operator<<(ostream & os, const Stock & st); //重载<<运算符
};
#endif
修改后 程序清单10.8
[code]// stock20.cpp -- augmented version
#include <iostream>
#include <cstring>
#include "stock20.h"
using namespace std;
// constructors
Stock::Stock() // default constructor
{
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)
{
std::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(const Stock & st) //复制构造函数
{
company = new char [strlen(st.company)+1];
strcpy(company, st.company);
shares = st.shares;
share_val = st.share_val;
total_val = st.share_val;
}
// class destructor
Stock::~Stock() // quiet class destructor
{
delete [] company;
}
// other methods
void Stock::buy(long num, double price)
{
if (num < 0)
{
std::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)
{
using std::cout;
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();
}
// void Stock::show() const
// {
// using std::cout;
// using std::ios_base;
/*set format to #.### */
// ios_base::fmtflags orig =
// cout.setf(ios_base::fixed, ios_base::floatfield);
// std::streamsize prec = cout.precision(3);
// cout << "Company: " << company
// << " Shares: " << shares << '\n';
// cout << " Share Price: $" << share_val;
/*set format to #.##*/
// cout.precision(2);
// cout << " Total Worth: $" << total_val << '\n';
/*restore original format*/
// cout.setf(orig, ios_base::floatfield);
// cout.precision(prec);
// }
const Stock & Stock::topval(const Stock & s) const
{
if (s.total_val > total_val)
return s;
else
return *this;
}
Stock & Stock::operator=(const Stock & st) //重载赋值运算符
{
if (this == &st)
return *this;
delete [] company;
company = new char [strlen(st.company)+1];
strcpy(company, st.company);
shares = st.shares;
share_val = st.share_val;
total_val = st.share_val;
return *this;
}
ostream & operator<<(ostream & os, const Stock & st)
{
using std::ios_base;
// set format to #.###
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;
}
修改后 程序清单10.9
[code]// usestok2.cpp -- using the Stock class
// compile with stock20.cpp
#include <iostream>
#include "stock20.h"
const int STKS = 4;
int main()
{
using namespace std;
// 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)
};
std::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
std::cout << "\nMost valuable holding:\n";
cout << *top;
// std::cin.get();
return 0;
}
4. 请看下面程序清单10.10 定义的Stack类的变量：
[code]// 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。
[code]// stack.h -- class declaration for the stack ADT
#include <iostream>
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);
friend std::ostream & operator<<(std::ostream & os, const Stack & st);
};
[code]// stack.cpp -- Stack member functions
#include <iostream>
#include "stack.h"
using namespace std;
Stack::Stack(int n)
{
size = n;
pitems = new Item [size];
for (int i = 0; i < size; i++)
pitems[i] = 0;
top = 0;
}
Stack::Stack(const Stack & st)
{
size = st.size;
pitems = new Item [size];
for (int i = 0; i < size; i++)
pitems[i] = st.pitems[i];
top = st.top;
}
Stack::~Stack()
{
delete [] pitems;
}
bool Stack::isempty() const
{
return top == 0;
}
bool Stack::isfull() const
{
return top == MAX;
}
bool Stack::push(const Item & item)
{
if (top < MAX)
{
pitems[top++] = item;
return true;
}
else
return false;
}
bool Stack::pop(Item & item)
{
if (top > 0)
{
item = pitems[--top];
return true;
}
else
return false;
}
Stack & Stack::operator=(const Stack & st)
{
if (this == &st)
return *this;
size = st.size;
pitems = new Item [size];
for (int i = 0; i < size; i++)
pitems[i] = st.pitems[i];
top = st.top;
return *this;
}
std::ostream & operator<<(std::ostream & os, const Stack & st)
{
for (int i = 0; i < st.top; i++)
cout << st.pitems[i] << endl;
return os;
}
[code]// stacker.cpp -- testing the Stack class
#include <iostream>
#include <cctype> // or ctype.h
#include "stack.h"
int main()
{
using namespace std;
Stack st;
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";
}
cout << "So our stack is:\n" << st;
Stack st2;
st2 = st;
cout << "stack2 = stack is:\n" << st2;
Stack st3 = st;
cout << "stack3 = stack is:\n" << st3;
cout << "Bye\n";
return 0;
}
5. Heather银行进行的研究表明，ATM客户不希望排队时间超过1分钟。使用程序清单12.10 中的模拟，
找出要使平均等候时间为1分钟，每小时到达的客户数应为多少（试验时间不短于100小时）？
程序清单12.10
[code]// 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
程序清单12.11
[code]// queue.cpp -- Queue and Customer methods
#include "queue.h"
#include <cstdlib> // (or stdlib.h) for rand()
// Queue methods
Queue::Queue(int qs) : qsize(qs) //构造函数
{
front = rear = NULL; // or nullptr
items = 0;
}
Queue::~Queue() //析构函数
{
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;
}
程序清单12.12
[code]// 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";
//请求输入队伍长度
cout << "Enter maximum size of queue: ";
int qs;
cin >> qs;
Queue line(qs); // line queue holds up to qs people
//请求输入模拟时间长度
cout << "Enter the number of simulation hours: ";
int hours; // hours of simulation
cin >> hours;
// simulation will run 1 cycle per minute 转换为分钟
long cyclelimit = MIN_PER_HR * hours; // # of cycles
//请求输入平均每小时的顾客数
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; //计算平均每分钟的顾客数
Item temp; // new customer data
long turnaways = 0; // turned away by full queue 被拒绝的顾客数
long customers = 0; // joined the queue 加入队列的顾客数
long served = 0; // served during the simulation 服务的顾客数
long sum_line = 0; // cumulative line length 累积的队列长度
int wait_time = 0; // time until autoteller is free 直到ATM空闲的时间
long line_wait = 0; // cumulative time in line 排队等候时间
// 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);
}
程序清单12.12 修改后
[code]// bank.cpp -- using the Queue interface
// compile with queue.cpp
#include <iostream>
#include <cstdlib>
#include <ctime>
#include "queue.h"
const int MIN_PER_HR = 60;
bool newcustomer(double x);
int main()
{
using std::cin;
using std::cout;
using std::endl;
using std::ios_base;
std::srand(std::time(0));
cout << "Case Study: Bank of Heather Automatic Teller\n";
cout << "Enter maximum size of queue: ";
int qs;
cin >> qs;
Queue line(qs);
cout << "The simulation hours: 100\n";
int hours = 100;
long cyclelimit = MIN_PER_HR * hours;
double perhour;
double min_per_cust;
perhour = 1;
Item temp;
long turnaways = 0;
long customers = 0;
long served = 0;
long sum_line = 0;
int wait_time = 0;
long line_wait = 0;
double avetime = 0;
while (avetime <= 1)
{
while (!line.isempty())
{
line.dequeue(temp);
}
min_per_cust = MIN_PER_HR / perhour;
for (int cycle = 0; cycle < cyclelimit; cycle++)
{
if (newcustomer(min_per_cust))
{
if (line.isfull())
turnaways++;
else
{
customers++;
temp.set(cycle);
line.enqueue(temp);
}
}
if (wait_time <= 0 && !line.isempty())
{
line.dequeue(temp);
wait_time = temp.ptime();
line_wait += cycle - temp.when();
served++;
}
if (wait_time > 0)
wait_time--;
sum_line += line.queuecount();
}
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";
avetime = (double)line_wait / served;
perhour++;
}
cout << "When there comes " << perhour << " people per hour, the average wait time will be about 1 minute.\n";
cout << "Done!\n";
system("pause");
return 0;
}
bool newcustomer(double x)
{
return (std::rand() * x / RAND_MAX < 1);
}
6. Heather银行想知道，如果再开设一台ATM，情况将如何。请对模拟进行修改，以包含两个队列。
假设当第一台ATM前的排队人数少于第二台ATM时，客户将排在第一队，否则将排在第二队。
然后再找出要使平均等候时间为1分钟，每小时到达的客户数应该为多少？
（注意这是一个非线性问题，即将ATM数量加倍，并不能保证每小时处理客户等候的时间少于1分钟）
[code]// bank.cpp -- using the Queue interface
// compile with queue.cpp
#include <iostream>
#include <cstdlib>
#include <ctime>
#include "queue.h"
const int MIN_PER_HR = 60;
bool newcustomer(double x);
int main()
{
using std::cin;
using std::cout;
using std::endl;
using std::ios_base;
std::srand(std::time(0));
cout << "Case Study: Bank of Heather Automatic Teller\n";
cout << "Enter maximum size of queue: ";
int qs;
cin >> qs;
Queue line1(qs);
Queue line2(qs);
cout << "The simulation hours: 100\n";
int hours = 100;
long cyclelimit = MIN_PER_HR * hours;
double perhour;
double min_per_cust;
perhour = 1;
Item temp;
long turnaways = 0;
long customers = 0;
long customers1 = 0;
long customers2 = 0;
long served = 0;
long sum_line = 0;
long sum_line1 = 0;
long sum_line2 = 0;
int wait_time = 0;
int wait_time1 = 0;
int wait_time2 = 0;
long line_wait = 0;
double avetime = 0;
while (perhour++ && avetime <= 1)
{
while (!line1.isempty())
{
line1.dequeue(temp);
}
while (!line2.isempty())
{
line2.dequeue(temp);
}
min_per_cust = MIN_PER_HR / perhour;
for (int cycle = 0; cycle < cyclelimit; cycle++)
{
if (newcustomer(min_per_cust))
{
if (line1.isfull() && line2.isfull())
turnaways++;
else
{
if(customers1 <= customers2)
{
customers++;
customers1++;
temp.set(cycle);
line1.enqueue(temp);
}
else
{
customers++;
customers2++;
temp.set(cycle);
line2.enqueue(temp);
}
}
}
if (wait_time1 <= 0 && !line1.isempty())
{
line1.dequeue(temp);
wait_time1 = temp.ptime();
line_wait += cycle - temp.when();
served++;
}
if (wait_time2 <= 0 && !line2.isempty())
{
line2.dequeue(temp);
wait_time2 = temp.ptime();
line_wait += cycle - temp.when();
served++;
}
if (wait_time1 > 0)
wait_time1--;
if (wait_time2 > 0)
wait_time2--;
sum_line1 += line1.queuecount();
sum_line2 += line1.queuecount();
sum_line = sum_line1 + sum_line2;
}
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";
avetime = (double)line_wait / served;
}
cout << "When there comes " << perhour << " people per hour, the average wait time will be about 1 minute.\n";
cout << "Done!\n";
system("pause");
return 0;
}
bool newcustomer(double x)
{
return (std::rand() * x / RAND_MAX < 1);
}
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