《C++ Primer Plus》
第12章 课后练习2
#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;
static const int CINLIM = 80;
public:
String(const char * s);
String();
String(const String &);
~String();
int length () const { return len; }
String & operator=(const String &);
String & operator=(const char *);
char & operator[](int i);
const char & operator[](int i) const;
void Stringlow();
void Stringup();
int has(const char c);
String operator+(const String & st1);
operator char *() const;
friend bool operator<(const String & st1, const String & st2);
friend bool operator>(const String & st1, const String & st2);
friend bool operator==(const String & st1, const String & st2);
friend String operator+(const char *, const String & st1);
friend ostream & operator<<(ostream & os, const String & st);
friend istream & operator>>(istream & is, String & st);
static int HowMany();
};
#endif
#include <cstring>
#include <cctype>
#include "String.h"
#include <iostream>
int String::num_strings = 0;
int String::HowMany()
{
return num_strings;
}
String::String(const char * s)
{
len = std::strlen(s);
str = new char[len+1];
std::strcpy(str,s);
num_strings++;
}
String::String()
{
len = 4;
str = new char[1];
str[0] = '\0';
num_strings++;
}
String::String(const String & st)
{
num_strings++;
len = st.len;
str = new char[len+1];
std::strcpy(str,st.str);
}
String::~String()
{
--num_strings;
delete [] str;
}
String & String::operator=(const String & st)
{
delete [] str;
len = strlen(st.str);
str = new char[len+1];
std::strcpy(str,st.str);
return *this;
}
String & String::operator=(const char * s)
{
delete [] str;
len = std::strlen(s);
str = new char[len+1];
std::strcpy(str, s);
return *this;
}
char & String::operator[](int i)
{
return str[i];
}
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);
}
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;
while (is && is.get() != '\n')
continue;
return is;
}
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]);
}
/* 错误的重载函数，问题是构造temp的时候，已经使用new 分配了固定长度的内存。使用strcat的时候实际上已经内存溢出了.
String String::operator+(const String & st1)
{
String temp(str);
strcat(temp.str,st1.str);
temp.len = strlen(str) + strlen(st1.str) + 1;
return temp;
}
*/
String String::operator+(const String & st1)
{
int nlen = strlen(st1.str) + strlen(str) + 1;
char * nstr = new char[nlen];
strcpy(nstr,str);
strcat(nstr,st1.str);
String temp;
delete [] temp.str;
temp.str = nstr;
return temp;
}
String::operator char *() const
{
return str;
}
String operator+(const char * st1,const String & st2)
{
String temp;
strcat(temp.str,st1);
strcat(temp.str,st2.str);
temp.len = strlen(st1) + st2.len;
return temp;
}
int String::has(const char c)
{
int count = 0;
for(int i = 0; i < len; i++)
if (str[i] == c )
count++;
return count;
}
#include <iostream>
using namespace std;
#include "String2.h"
int main()
{
String s1(" and I am C++ stdudent.");
String s2 = "Pleas enter your name: ";
String s3;
cout << s2;
cin >> s3;
s2 = "My name is " + s3;
cout << s2 << ".\n";
s2 = s2 + s1;
s2.Stringup();
cout << "The string\n" << s2 << "\ncontains " << s2.has('A')
<< " 'A' characters in it.\n";
s1 = "red";
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();
for(int i = 0; i < 3; i++)
{
if(ans == rgb[i])
{
cout << "That's right!\n";
success = true;
break;
}
}
if (success)
break;
else
cout << "Try again!\n";
}
cout << "Bye\n";
return 0;
}
第12章 课后练习6
#ifndef QUEUE_H_
#define QUEUE_H_
class Customer
{
private:
long arrive;
int processtime;
public:
Customer() { arrive = processtime = 0; }
void set(long when);
long when() const { return arrive; }
int ptime() const { return processtime; }
};
typedef Customer Item;
class Queue
{
private:
struct Node { Item item; struct Node * next ; };
enum { Q_SIZE = 10 };
Node * front;
Node * rear;
int items;
const int qsize;
Queue(const Queue & q) : qsize(0) { }
Queue & operator=(const Queue & q) { return *this; }
public:
Queue( int qs = Q_SIZE );
~Queue();
bool isempty() const;
bool isfull() const;
int queuecount() const;
bool enqueue(const Item & item);
bool dequeue(Item & item);
};
#endif
#include "queue.h"
#include <cstdlib>
#include <stdio.h>
Queue::Queue(int qs) : qsize(qs)
{
front = rear = NULL;
items = 0;
}
Queue::~Queue()
{
Node * temp;
while(front != NULL)
{
temp = front;
front = front->next;
delete temp;
}
}
bool Queue::isempty() const
{
return items == 0;
}
bool Queue::isfull() const
{
return items == qsize;
}
int Queue::queuecount() const
{
return items;
}
bool Queue::enqueue(const Item & item)
{
if (isfull())
return false;
Node * add = new Node;
add->item = item;
add->next = NULL;
items++;
if(front == NULL)
front = add;
else
rear->next = add;
rear = add;
return true;
}
bool Queue::dequeue(Item & item)
{
if(front == NULL)
return false;
item = front->item;
items--;
Node * temp = front;
front = front->next;
delete temp;
if(items == 0)
rear = NULL;
return true;
}
void Customer::set(long when)
{
processtime = std::rand() % 3 + 1;
arrive = when;
}
[code lang="C" title="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 << "Enter the number of simulation hours: ";
int hours;
cin >> hours;
long cyclelimit = MIN_PER_HR * hours;
cout << "Enter the average number of customers per hours: ";
double perhour;
cin >> perhour;
double min_per_cust;
min_per_cust = MIN_PER_HR / perhour ;
Item temp1,temp2;
long turnaways = 0;
long customers = 0;
long served = 0;
long sum_line = 0;
int wait_time1,wait_time2;
wait_time1 = wait_time2 = 0;
long line_wait = 0;
for(int cycle = 0;cycle < cyclelimit; cycle++)
{
if (newcustomer(min_per_cust))
{
if ( line1.isfull() && line2.isfull() )
turnaways++;
else
{
customers++;
if ( line1.isfull() )
{
temp2.set(cycle);
line2.enqueue(temp2);
}
else
{
temp1.set(cycle);
line1.enqueue(temp1);
}
}
}
if (wait_time1 <= 0 && !line1.isempty())
{
line1.dequeue(temp1);
wait_time1 = temp1.ptime();
line_wait += cycle - temp1.when();
served++;
}
if (wait_time2 <= 0 && !line2.isempty())
{
line2.dequeue(temp2);
wait_time2 = temp2.ptime();
line_wait += cycle - temp2.when();
served++;
}
if(wait_time1 > 0)
wait_time1--;
if(wait_time2 > 0)
wait_time2--;
sum_line += ( line1.queuecount() + line2.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";
cout << "Done!\n";
return 0;
}
bool newcustomer(double x)
{
return (std::rand() * x / RAND_MAX < 1);
}