C++ primer plus(第六版)编程练习答案第6章分支语句和逻辑运算符

港控/mmm° 2024-03-24 08:34 7阅读 0赞

## 一、程序清单 ##

## if.cpp ##

// if.cpp -- using the if statement
    #include <iostream>
    int main()
    {
    	using std::cin;     // using declarations
    	using std::cout;
    	char ch;
    	int spaces = 0;
    	int total = 0;
    	cin.get(ch);
    	while (ch != '.')   // quit at end of sentence
    	{
    		if (ch == ' ')  // check if ch is a space
    			++spaces;
    		++total;        // done every time
    		cin.get(ch);
    	}
    	cout << spaces << " spaces, " << total;
    	cout << " characters total in sentence\n";
    	// cin.get();
    	// cin.get();
    	return 0;
    }

执行结果：

The balloonist was an airhead
    with lofty goals.
    7 spaces, 47 characters total in sentence

## ifelse.cpp ##

// ifelse.cpp -- using the if else statement
    #include <iostream>
    int main()
    {
    	char ch;
    
    	std::cout << "Type, and I shall repeat.\n";
    	std::cin.get(ch);
    	while (ch != '.')
    	{
    		if (ch == '\n')
    			std::cout << ch;     // done if newline
    		else
    			std::cout << ++ch;   // done otherwise
    		std::cin.get(ch);
    	}
    	// try ch + 1 instead of ++ch for interesting effect
    	std::cout << "\nPlease excuse the slight confusion.\n";
    	// std::cin.get();
    	// std::cin.get();
    	return 0;
    }

执行结果:

Type, and I shall repeat.
    An ineffable joy suffused me as I beheld
    Bo!jofggbcmf!kpz!tvggvtfe!nf!bt!J!cfifme
    the wonders of modern computing.
    uif!xpoefst!pg!npefso!dpnqvujoh
    Please excuse the slight confusion.

## ifelseif.cpp ##

// ifelseif.cpp -- using if else if else
    #include <iostream>
    const int Fave = 27;
    int main()
    {
        using namespace std;
        int n;
    
        cout << "Enter a number in the range 1-100 to find ";
        cout << "my favorite number: ";
        do
        {
            cin >> n;
            if (n < Fave)
                cout << "Too low -- guess again: ";
            else if (n > Fave)
                cout << "Too high -- guess again: ";
            else
                cout << Fave << " is right!\n";
        } while (n != Fave);
        // cin.get();
        // cin.get();
        return 0;
    }

执行结果：

Enter a number in the range 1-100 to find my favorite number: 50
    Too high -- guess again: 28
    Too high -- guess again: 27
    27 is right!

## or.cpp ##

// or.cpp -- using the logical OR operator
    #include <iostream>
    int main()
    {
    	using namespace std;
    	cout << "This program may reformat your hard disk\n"
    		"and destroy all your data.\n"
    		"Do you wish to continue? <y/n> ";
    	char ch;
    	cin >> ch;
    	if (ch == 'y' || ch == 'Y')             // y or Y
    		cout << "You were warned!\a\a\n";
    	else if (ch == 'n' || ch == 'N')        // n or N
    		cout << "A wise choice ... bye\n";
    	else
    		cout << "That wasn't a y or n! Apparently you "
    		"can't follow\ninstructions, so "
    		"I'll trash your disk anyway.\a\a\a\n";
    	// cin.get();
    	// cin.get();
    	return 0;
    }

执行结果：

This program may reformat your hard disk
    and destroy all your data.
    Do you wish to continue? <y/n> n
    A wise choice ... bye

## and.cpp ##

// and.cpp -- using the logical AND operator
    #include <iostream>
    const int ArSize = 6;
    int main()
    {
    	using namespace std;
    	float naaq[ArSize];
    	cout << "Enter the NAAQs (New Age Awareness Quotients) "
    		<< "of\nyour neighbors. Program terminates "
    		<< "when you make\n" << ArSize << " entries "
    		<< "or enter a negative value.\n";
    
    	int i = 0;
    	float temp;
    	cout << "First value: ";
    	cin >> temp;
    	while (i < ArSize && temp >= 0) // 2 quitting criteria
    	{
    		naaq[i] = temp;
    		++i;
    		if (i < ArSize)             // room left in the array,
    		{
    			cout << "Next value: ";
    			cin >> temp;            // so get next value
    		}
    	}
    	if (i == 0)
    		cout << "No data--bye\n";
    	else
    	{
    		cout << "Enter your NAAQ: ";
    		float you;
    		cin >> you;
    		int count = 0;
    		for (int j = 0; j < i; j++)
    			if (naaq[j] > you)
    				++count;
    		cout << count;
    		cout << " of your neighbors have greater awareness of\n"
    			<< "the New Age than you do.\n";
    	}
    	// cin.get();
    	// cin.get();
    	return 0;
    }

## and.cpp ##

执行结果：

Enter the NAAQs (New Age Awareness Quotients) of
    your neighbors. Program terminates when you make
    6 entries or enter a negative value.
    First value: 28
    Next value: 72
    Next value: 15
    Next value: 6
    Next value: 130
    Next value: 145
    Enter your NAAQ: 50
    3 of your neighbors have greater awareness of
    the New Age than you do.

## more\_and.cpp ##

// more_and.cpp -- using the logical AND operator
    #include <iostream>
    const char * qualify[4] =       // an array of pointers*/
    {                               // to strings
        "10,000-meter race.\n",
        "mud tug-of-war.\n",
        "masters canoe jousting.\n",
        "pie-throwing festival.\n"
    };
    int main()
    {
        using namespace std;
        int age;
        cout << "Enter your age in years: ";
        cin >> age;
        int index;
    
        if (age > 17 && age < 35)
            index = 0;
        else if (age >= 35 && age < 50)
            index = 1;
        else if (age >= 50 && age < 65)
            index = 2;
        else
            index = 3;
    
        cout << "You qualify for the " << qualify[index]; 
        // cin.get();
        // cin.get();
        return 0;
    }

执行结果：

Enter your age in years: 87
    You qualify for the pie-throwing festival.

## not.cpp ##

// not.cpp -- using the not operator
    #include <iostream>
    #include <climits>
    bool is_int(double);
    int main()
    {
    	using namespace std;
    	double num;
    
    	cout << "Yo, dude! Enter an integer value: ";
    	cin >> num;
    	while (!is_int(num))    // continue while num is not int-able
    	{
    		cout << "Out of range -- please try again: ";
    		cin >> num;
    	}
    	int val = int(num);    // type cast
    	cout << "You've entered the integer " << val << "\nBye\n";
    	// cin.get();
    	// cin.get();
    	return 0;
    }
    
    bool is_int(double x)
    {
    	if (x <= INT_MAX && x >= INT_MIN)   // use climits values
    		return true;
    	else
    		return false;
    }

执行结果：

Yo, dude! Enter an integer value: 6234128679
    Out of range -- please try again: -8000222333
    Out of range -- please try again: 99999
    You've entered the integer 99999
    Bye

## cctypes.cpp ##

// cctypes.cpp -- using the ctype.h library
    #include <iostream>
    #include <cctype>              // prototypes for character functions
    int main()
    {
        using namespace std;
        cout << "Enter text for analysis, and type @"
                " to terminate input.\n";
        char ch;  
        int whitespace = 0;
        int digits = 0;
        int chars = 0;
        int punct = 0;
        int others = 0;
    
        cin.get(ch);                // get first character
        while (ch != '@')            // test for sentinel
        {
            if(isalpha(ch))         // is it an alphabetic character?
                chars++;
            else if(isspace(ch))    // is it a whitespace character?
                whitespace++;
            else if(isdigit(ch))    // is it a digit?
                digits++;
            else if(ispunct(ch))    // is it punctuation?
                punct++;
            else
                others++;
            cin.get(ch);            // get next character
        }
        cout << chars << " letters, "
             << whitespace << " whitespace, "
             << digits << " digits, "
             << punct << " punctuations, "
             << others << " others.\n";
        // cin.get();
        // cin.get();
        return 0; 
    }

执行结果：

Enter text for analysis, and type @ to terminate input.
    AdrenalVision International producer Adrienne Vismonger
    announced production of their new 3-D film,a remark of
    "My Dinner with Andre," scheduled for 2013."Wait until
    you see the new scene with an enraged Collossipede!"@
    174 letters, 32 whitespace, 5 digits, 9 punctuations, 0 others.

## condit.cpp ##

// condit.cpp -- using the conditional operator
    #include <iostream>
    int main()
    {
    	using namespace std;
    	int a, b;
    	cout << "Enter two integers: ";
    	cin >> a >> b;
    	cout << "The larger of " << a << " and " << b;
    	int c = a > b ? a : b;   // c = a if a > b, else c = b
    	cout << " is " << c << endl;
    	// cin.get();
    	// cin.get();
    	return 0;
    }

执行结果：

Enter two integers: 25 28
    The larger of 25 and 28 is 28

## switch.cpp ##

// switch.cpp -- using the switch statement
    #include <iostream>
    using namespace std;
    void showmenu();   // function prototypes
    void report();
    void comfort();
    int main()
    {
        showmenu();
        int choice;
        cin >> choice;
        while (choice != 5)
        {
            switch(choice)
            {
                case 1  :   cout << "\a\n";
                            break;
                case 2  :   report();
                            break;
                case 3  :   cout << "The boss was in all day.\n";
                            break;
                case 4  :   comfort();
                            break;
                default :   cout << "That's not a choice.\n";
            }
            showmenu();
            cin >> choice;
        }
        cout << "Bye!\n";
        // cin.get();
        // cin.get();
        return 0;
    }
    
    void showmenu()
    {
        cout << "Please enter 1, 2, 3, 4, or 5:\n"
                "1) alarm           2) report\n"
                "3) alibi           4) comfort\n"
                "5) quit\n";
    }
    void report()
    {
        cout << "It's been an excellent week for business.\n"
            "Sales are up 120%. Expenses are down 35%.\n";
    }
    void comfort()
    {
        cout << "Your employees think you are the finest CEO\n"
            "in the industry. The board of directors think\n"
            "you are the finest CEO in the industry.\n";
    }

执行结果：

Please enter 1, 2, 3, 4, or 5:
    1) alarm           2) report
    3) alibi           4) comfort
    5) quit
    4
    Your employees think you are the finest CEO
    in the industry. The board of directors think
    you are the finest CEO in the industry.
    Please enter 1, 2, 3, 4, or 5:
    1) alarm           2) report
    3) alibi           4) comfort
    5) quit
    2
    It's been an excellent week for business.
    Sales are up 120%. Expenses are down 35%.
    Please enter 1, 2, 3, 4, or 5:
    1) alarm           2) report
    3) alibi           4) comfort
    5) quit
    6
    That's not a choice.
    Please enter 1, 2, 3, 4, or 5:
    1) alarm           2) report
    3) alibi           4) comfort
    5) quit
    5
    Bye!

## enum.cpp ##

// enum.cpp -- using enum
    #include <iostream>
    // create named constants for 0 - 6
    enum { red, orange, yellow, green, blue, violet, indigo };
    
    int main()
    {
    	using namespace std;
    	cout << "Enter color code (0-6): ";
    	int code;
    	cin >> code;
    	while (code >= red && code <= indigo)
    	{
    		switch (code)
    		{
    		case red: cout << "Her lips were red.\n"; break;
    		case orange: cout << "Her hair was orange.\n"; break;
    		case yellow: cout << "Her shoes were yellow.\n"; break;
    		case green: cout << "Her nails were green.\n"; break;
    		case blue: cout << "Her sweatsuit was blue.\n"; break;
    		case violet: cout << "Her eyes were violet.\n"; break;
    		case indigo: cout << "Her mood was indigo.\n"; break;
    		}
    		cout << "Enter color code (0-6): ";
    		cin >> code;
    	}
    	cout << "Bye\n";
    	// cin.get();
    	// cin.get();
    	return 0;
    }

执行结果：

Enter color code (0-6): 3
    Her nails were green.
    Enter color code (0-6): 5
    Her eyes were violet.
    Enter color code (0-6): 2
    Her shoes were yellow.
    Enter color code (0-6): 8
    Bye

## jump.cpp ##

// jump.cpp -- using continue and break
    #include <iostream>
    const int ArSize = 80;
    int main()
    {
        using namespace std;
        char line[ArSize];
        int spaces = 0; 
    
        cout << "Enter a line of text:\n";
        cin.get(line, ArSize);
        cout << "Complete line:\n" << line << endl;
        cout << "Line through first period:\n";
        for (int i = 0; line[i] != '\0'; i++)
        {
            cout << line[i];    // display character
            if (line[i] == '.') // quit if it's a period
                break;
            if (line[i] != ' ') // skip rest of loop
                continue;
            spaces++;
        }
        cout << "\n" << spaces << " spaces\n";
        cout << "Done.\n";
        // cin.get();
        // cin.get();
        return 0;
    }

执行结果：

Enter a line of text:
    Let's do lunch today.You can pay!
    Complete line:
    Let's do lunch today.You can pay!
    Line through first period:
    Let's do lunch today.
    3 spaces
    Done.

## cinfish.cpp ##

// cinfish.cpp -- non-numeric input terminates loop
    #include <iostream>
    const int Max = 5;
    int main()
    {
        using namespace std;
    // get data
        double fish[Max];
        cout << "Please enter the weights of your fish.\n";
        cout << "You may enter up to " << Max
                << " fish <q to terminate>.\n";
        cout << "fish #1: ";
        int i = 0;
        while (i < Max && cin >> fish[i]) {
            if (++i < Max)
                cout << "fish #" << i+1 << ": ";
        }
    // calculate average
        double total = 0.0;
        for (int j = 0; j < i; j++)
            total += fish[j];
    // report results
        if (i == 0)
            cout << "No fish\n";
        else
            cout << total / i << " = average weight of "
                << i << " fish\n";
        cout << "Done.\n";
    // code to keep VC execution window open if q is entered
    //	if (!cin)  // input terminated by non-numeric response
    //	{
    //	    cin.clear();  // reset input
    //	    cin.get();    // read q
    //	}
    //	cin.get();    // read end of line after last input
    //	cin.get();    // wait for user to press <Enter>
        return 0; 
    }

执行结果：

Please enter the weights of your fish.
    You may enter up to 5 fish <q to terminate>.
    fish #1: 30
    fish #2: 25
    fish #3: 25
    fish #4: 40
    fish #5: q
    30 = average weight of 4 fish
    Done.

## cingolf.cpp ##

// cingolf.cpp -- non-numeric input skipped
    #include <iostream>
    const int Max = 5;
    int main()
    {
    	using namespace std;
    	// get data
    	int golf[Max];
    	cout << "Please enter your golf scores.\n";
    	cout << "You must enter " << Max << " rounds.\n";
    	int i;
    	for (i = 0; i < Max; i++)
    	{
    		cout << "round #" << i + 1 << ": ";
    		while (!(cin >> golf[i])) {
    			cin.clear();     // reset input
    			while (cin.get() != '\n')
    				continue;    // get rid of bad input
    			cout << "Please enter a number: ";
    		}
    	}
    	// calculate average
    	double total = 0.0;
    	for (i = 0; i < Max; i++)
    		total += golf[i];
    	// report results
    	cout << total / Max << " = average score "
    		<< Max << " rounds\n";
    	// cin.get();
    	// cin.get();
    	return 0;
    }

执行结果：

Please enter your golf scores.
    You must enter 5 rounds.
    round #1: 88
    round #2: 87
    round #3: must i?
    Please enter a number: 103
    round #4: 94
    round #5: 86
    91.6 = average score 5 rounds

## outfile.cpp ##

// outfile.cpp -- writing to a file
    #include <iostream>
    #include <fstream>                  // for file I/O
    
    int main()
    {
    	using namespace std;
    
    	char automobile[50];
    	int year;
    	double a_price;
    	double d_price;
    
    	ofstream outFile;               // create object for output
    	outFile.open("carinfo.txt");    // associate with a file
    
    	cout << "Enter the make and model of automobile: ";
    	cin.getline(automobile, 50);
    	cout << "Enter the model year: ";
    	cin >> year;
    	cout << "Enter the original asking price: ";
    	cin >> a_price;
    	d_price = 0.913 * a_price;
    
    	// display information on screen with cout
    
    	cout << fixed;
    	cout.precision(2);
    	cout.setf(ios_base::showpoint);
    	cout << "Make and model: " << automobile << endl;
    	cout << "Year: " << year << endl;
    	cout << "Was asking $" << a_price << endl;
    	cout << "Now asking $" << d_price << endl;
    
    	// now do exact same things using outFile instead of cout
    
    	outFile << fixed;
    	outFile.precision(2);
    	outFile.setf(ios_base::showpoint);
    	outFile << "Make and model: " << automobile << endl;
    	outFile << "Year: " << year << endl;
    	outFile << "Was asking $" << a_price << endl;
    	outFile << "Now asking $" << d_price << endl;
    
    	outFile.close();                // done with file
    	// cin.get();
    	// cin.get();
    	return 0;
    }

执行结果：

Enter the make and model of automobile: Flitz Perky
    Enter the model year: 2009
    Enter the original asking price: 13500
    Make and model: Flitz Perky
    Year: 2009
    Was asking $13500.00
    Now asking $12325.508

## sumafile.cpp ##

建立一个scores.txt文档：

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA6ZW_5rKZ5pyJ6IKl6bG8_size_20_color_FFFFFF_t_70_g_se_x_16][]

// sumafile.cpp -- functions with an array argument
    #include <iostream>
    #include <fstream>          // file I/O support
    #include <cstdlib>          // support for exit()
    const int SIZE = 60;
    int main()
    {
        using namespace std;
        char filename[SIZE];
        ifstream inFile;        // object for handling file input
    
        cout << "Enter name of data file: ";
        cin.getline(filename, SIZE);
        inFile.open(filename);  // associate inFile with a file
        if (!inFile.is_open())  // failed to open file
        {
            cout << "Could not open the file " << filename << endl;
            cout << "Program terminating.\n";
            // cin.get();    // keep window open
            exit(EXIT_FAILURE);
        }
        double value;
        double sum = 0.0;
        int count = 0;          // number of items read
    
        inFile >> value;        // get first value
        while (inFile.good())   // while input good and not at EOF
        {
            ++count;            // one more item read
            sum += value;       // calculate running total
            inFile >> value;    // get next value
        }
        if (inFile.eof())
            cout << "End of file reached.\n";
        else if (inFile.fail())
            cout << "Input terminated by data mismatch.\n";
        else
            cout << "Input terminated for unknown reason.\n";
        if (count == 0)
            cout << "No data processed.\n";
        else
        {
            cout << "Items read: " << count << endl;
            cout << "Sum: " << sum << endl;
            cout << "Average: " << sum / count << endl;
        }
        inFile.close();         // finished with the file
        // cin.get();
        return 0;
    }

执行结果：

Enter name of data file: scores.txt
    End of file reached.
    Items read: 11
    Sum: 187
    Average: 17

## 二、复习题 ##

1.请看下面两个计算空格和换行符数目的代码片段：

//version 1
    while(cin.get(ch))   //quit on eof
    {  
        if(ch==' ')
             spaces++;
        if(ch=='\n')
             newlines++;
    }
    
    //version 2
    while(cin.get(ch))   //quit eof
    {
        if(ch==' ')
             spacees++;
        else if(ch=='\n')    
             newlines++;
    }

第二个格式比第一个格式好在哪里？

第二个版本比第一个版本效率更高，因为在第一个中对于每个字符都需要判断两次，而在第二个版本中，如果字符为空格，在经过if判断确定为空格后，该字符肯定不是换行符，第二个else if的判断直接跳过，节省判断时间。

2.在程序清单6.2中，用ch+1替换++ch将发生什么情况？

程序清单6.2 ifelse.cpp

// ifelse.cpp -- using the if else statement
    #include <iostream>
    int main()
    {
       char ch;
       std::cout << "Type, and I shall repeat.\n";
       std::cin.get(ch);
       while (ch != '.')
       {
           if (ch == '\n')
                std::cout << ch; // done if newline
           else
                std::cout << ++ch; // done otherwise
           std::cin.get(ch);
    }
       // try ch + 1 instead of ++ch for interesting effect
       std::cout << "\nPlease excuse the slight confusion.\n";
       // std::cin.get();
       // std::cin.get();
       return 0;
    }

\++ch的数据类型依旧是char型，但对于char+1最终类型为int型，因此当++ch换成ch+1后，输出的是数字。

3.请认真考虑下面的程序：

#include<iostream>
    using namespace std;
    int main()
    {
        char ch;
        int ct1,ct2;
        ct1=ct2=0;
        while((ch=cin.get())!='$')
        {
            cout<<ch;
            ct1++;
            if(ch='$')
                  ct2++;
             cout<<ch;
        }
        cout<<"ct1="<<ct1<<",ct2="<<ct2<<"\n";
        return 0;
    }

假设输入如下（请在每行末尾按回车键）：

`Hi!`  
`Send $10 or $20 now!`

则输出将是什么（还记得吗，输入被缓冲）？

输入输出结果为

Hi!
    H$i$!$
    $Send $10 or $20 now!
    S$e$n$d$ $ct1=9,ct2=9

由于程序中使用的是`ch='$'`,所以每次循环该if条件内代码都执行一次，因此ct1与ct2相等。同时在输入`Hi!`之后键入回车，因此在读取回车之后，打印出来，光标换行，紧接着打印$。

4.创建表示下述条件的逻辑表达式：

**a.weight大于或等于115，但小于125。**  
**b.ch为q或Q。**  
**c.x为偶数，但不是26.**  
**d.x为偶数，但不是26。**  
**e.donation为1000-2000或guest为1。**  
**f.ch是小写字母或大写字母（假设小写字母是依次编码的，大写字母也是依次编码的，但在大小写字母间编码是不连续的）。**

//a
    weight>=115 && weight<125   
    
    //b
    ch=='q' || ch=='Q'
    
    //c
    x%2==0 && x!=26
    
    //d
    x%2==0 && x%26!=0
    
    //e
    donation>=1000 && donation<=20000 || guest==1
    
    //f
    (ch>='a' && ch<='z') || (ch<='Z' && ch>='A')

5.在英语中，"I will not not speak（我不会不说） "的意思与"I will speak（我要说）"相同。在c++中，!!x是否与x相同呢？

对于bool变量而言，!!x与x是相同的，但对于其他类型变量不一定相同，例如!!5=1，!!5≠5。

6.创建一个条件表达式，其值为变量的绝对值。也就是说，如果变量x为正，则表达式的值为x；但如果x为负，则表达式的值为-x--这是一个正值。

x>=0 ? x : -x;

7.用switch改写下面的代码片段：

if(ch=='A')
        a_grade++;
    else if(ch=='B')
        b_grade++;
    else if(ch=='C')
        c_grade++;
    else if(ch=='D')
        d_grade++;
    else
        f_grade++;

改写后代码：

switch(ch)
    {
        case 'A' : a_grade++;
                        break;
        case 'B' : b_grade++;
                        break;
        case 'C' : c_grade++;
                        break;
        case 'D' : d_grade++;
                        break;
        default :   f_grade++;
                        break;
    }

8.对于程序清单6.10，与使用字符（如a和c）表示菜单选项和case标签有何优点呢？（提示：想一想用户输入q和输入5的情况。）

> 程序清单6.10 switch.cpp
> 
>     // switch.cpp -- using the switch statement
>     #include <iostream>
>     using namespace std;
>     void showmenu(); // function prototypes
>     void report();
>     void comfort();
>     int main()
>     {
>        showmenu();
>        int choice;
>        cin >> choice;
>        while (choice != 5)
>        {
>            switch (choice)
>            {
>            case 1: cout << "\a\n";
>                break;
>            case 2: report();
>                break;
>            case 3: cout << "The boss was in all day.\n";
>                break;
>            case 4: comfort();
>                break;
>            default: cout << "That's not a choice.\n";
>            }
>            showmenu();
>            cin >> choice;
>        }
>        cout << "Bye!\n";
>        return 0;
>     }
>     void showmenu()
>     {
>        cout << "Please enter 1, 2, 3, 4, or 5:\n"
>            "1) alarm 2) report\n"
>            "3) alibi 4) comfort\n"
>            "5) quit\n";
>     }
>     void report()
>     {
>        cout << "It's been an excellent week for business.\n"
>            "Sales are up 120%. Expenses are down 35%.\n";
>     }
>     void comfort()
>     {
>        cout << "Your employees think you are the finest CEO\n"
>            "in the industry. The board of directors think\n"
>            "you are the finest CEO in the industry.\n";
>     }
> 
> 使用数字作为菜单选项和case标签，限定了用户只有输入数字的时候才能有效，若用户错误的输入非整数类型，导致程序被挂起。而使用字符作为菜单选项和case标签，当用户输入错误类型，程序能正确通过default部分提示用户输入错误，用户体验更加友好，提高了程序的容错性和健壮性。

9.请看下面的代码片段

int line = 0;
    char ch;
    while(cin.get(ch))
    {
        if(ch=='Q')
            break;
        if(ch!='\n')
            continue;
        line++;
    }

重写后代码：

int line = 0;
    char ch;
    while(cin.get(ch) && ch!='Q')
    {
        if(ch=='\n')
            line++;
    }

## 三、编程练习 ##

1.编写一个程序，读取键盘输入，直到遇到@符号为止，并回显输入（数字除外），同时将大写字符转换为小写字符，将小写字符转换为大写（别忘了cctype函数系列）

#include<iostream>
    #include<cctype>
    using namespace std;
    
    int main()
    {
        cout << "Please enter characters (type @ to stop):";
        char ch;
        cin.get(ch);
        while (ch != '@')
        {
            if (islower(ch))
                ch = toupper(ch);
            else if (isupper(ch))
                ch = tolower(ch);
            if (!isdigit(ch))
                cout << ch;
            cin.get(ch);
        }
        system("pause");
        return 0;
    }

2.编写一个程序，最多将10个donation值读入一个double数组中（如果你愿意，也可以使用模板类array）。程序遇到非数字输入时将结束输入，并报告这些数字的平均值以及数组中有多少个数字大于平均值。

#include<iostream>
    #include<array>
    using namespace std;
    int main()
    {
        array<double,10>donations;
        double sum=0;
        cout<<"Please enter donation(non-number to stop):";
        int i;
        double donation;
        for(i=0;(i<10)&&(cin>>donation);++i)
        {
            donations[i]=donation;
            sum=+donations[i];
        }    
    
        double avg=sum/(i+1);
        cout<<"Average:"<<avg<<endl;
        cout<<"Number larger than average:";
        for(int j=0;j<i;j++)
         {
            if(donations[j]>avg)
                cout<<donations[j]<<" ";
         }   
        cout<<endl;
        return 0;
    }

3.编写一个菜单驱动程序的雏形。该程序显示一个提供四个选项的菜单--每个选项用一个字母表标记。如果用户使用有效选项之外的字母进行响应，程序将提示用户输入有效的字母，直到用户这样选择为止。然后，该程序使用一条switch语句，根据用户的选择执行一个简单操作。该程序的运行情况如下：

Please enter one of the following choices:
    c) carnivore         p) pianist
    t) tree                  g)game
    f
    Please enter a c,p,t or g:q
    Please enter a c,p,t or g:t
    A maple is a tree.

代码实现：

#include <iostream>
    using namespace std;
    int main()
    {
        cout<<"Please enter one of the following choices:"<<endl;
        cout<<"c) carnivore         p) pianist"<<endl;
        cout<<"t) tree              g) game"<<endl;
        char ch;
        cin>>ch;
        while(ch!='c' && ch!='p' && ch!='t' && ch!='g')
        { 
            cout<<"Please enter a c,p,t or g:";
            cin>>ch;
        }   
        switch (ch)
        {
            case 'c':
                cout<<"A maple is a carnivore."<<endl;
                break;
            case 'p':
                cout<<"A maple is a pianist."<<endl;
                break;
            case 't':
                cout<<"A maple is a tree."<<endl;
                break;
            case 'g':
                cout<<"A maple is a game."<<endl;
                break;
            default:
                break;
        }
        return 0;
    }

4.加入Benevolent Order of Programmer后，在BOP大会上，人们便可以通过加入者的真实姓名、头衔或秘密BOP姓名来了解他（她）。请编写一个程序，可以使用真实姓名、头衔、秘密姓名或成员偏好来列出成员。编写该程序时，请使用下面的结构：

//Benevolent Order of Programmers name structure
    struct bop{
        char fullname[strsize];     //real name
        char title[strzie];              //job title
        char bopname[strsize];   //secret BOP name
        int preference;                //0=fullname,1=title,2=bopname
    };

该程序创建一个由上述结构组成的小型数组，并将其初始化为适当的值。另外，该程序使用一个循环，让用户在下面的选项中进行选择：

a.display by name        b.diaplay by title
    c.display by bopname     d.display by preference
    q.quit

注意，“display by preference”并不意味显示成员的偏好，而是意味着根据成员的偏好来列出成员。例如，如果偏好号为1，则选择d将显示程序员的头衔。该程序的运行情况如下：

Benevolent Order of Programmers Report
    a. display by name         b. display by title
    c. display by bopname      d. display by preference
    q. quit
    Enter your choice: a
    Wimp Macho
    Raki Rhodes
    Celia Laiter
    Hoppy Hipman
    Pat Hand
    Next choice: d
    Wimp Macho
    Junior Programmer
    MIPS
    Analyst Trainee
    LOOPY
    Next choice: q
    Bye!

代码实现 ：

#include <iostream>
    
    using namespace std;
    
    const int strsize = 20;
    struct bop
    {
        char fullname[strsize];
        char title[strsize];
        char bopname[strsize];
        int preference;         //0 = fullname, 1 = title, 2 = bopname
    };
    
    int main()
    {
        int programmerNum = 5;
        bop programmers[programmerNum]={
       {"Wimp Macho", "Junior Programmer", "WM",0},
        {"Raki Rhodes", "Junior Programmer", "RR", 1},
        {"Celia Laiter", "Junior Programmer", "MIPS", 2},
        {"Hoppy Hipman", "Analyst Trainee", "HH", 1},
        {"Pat Hand", "Junior Programmer", "LOOPY", 2}};
        cout << "Benevolent Order of Programmers Report" << endl;
        cout << "a. display by name          b. display by title" << endl;
        cout << "c. display by bopname       d. display by preference" << endl;
        cout << "q. quit" << endl;
        cout << "Enter your choice: ";
        char choice;
        while(cin.get(choice))
        {
            if(choice == 'a')
            {
                for(int i = 0; i < programmerNum; i++)
                {
                    cout << programmers[i].fullname << endl;
                }
            }
            else if(choice == 'b')
            {
                for(int i = 0; i < programmerNum; i++)
                {
                    cout << programmers[i].title << endl;
                }
            }
            else if(choice == 'c')
            {
                for(int i = 0; i < programmerNum; i++)
                {
                    cout << programmers[i].bopname << endl;
                }
            }
            else if(choice == 'd')
            {
                for(int i = 0; i < programmerNum; i++)
                {
                    if(programmers[i].preference == 0)
                    {
                        cout << programmers[i].fullname << endl;
                    }
                    else if(programmers[i].preference == 1)
                    {
                        cout << programmers[i].title << endl;
                    }
                    else
                    {
                        cout << programmers[i].bopname << endl;
                    }
                }
            }
            else if(choice == 'q')
            {
                cout << "Bye!" << endl;
                break;
            }
            else
            {
                if(choice == '\n')
                {
                    continue;
                }
                cout << "input error, please re-enter!" << endl;
            }
            cout << "Next choice: ";
        }
    
        return 0;
    }

5.在Neutronia王国,货币单位是tvarp,收入所得税的计算方式如下:

`5000 tvarps: 不收税`  
`5001－15000 tvarps: 10%`  
`15001－35000 tvarps: 15%`  
`35000 tvarps以上: 20%`

例如,收入为38000 tvarps时,所得税为5000×0.00+10000×0.10+2000×0.15+3000×0.20,即 4600tvarps。请编写一个程序，使用循环来要求用户输入收入，并报告所得税，当用户输入负数或非数字时，循环将结束。

代码实现：

#include<iostream>
    
    using namespace std;
    
    int main()
    {
        cout << "Please enter your income(if you enter negative number or non-numberic, it will exit.) : ";
        double income, tax;
        while(cin >> income)
        {
            cout<< income <<endl;
            if(income > 35000)
            {
                tax = 10000 * 0.10 + 20000 * 0.15 + (income - 35000) * 0.20;
            }
            else if(income >= 15001)
            {
                tax = (income - 3500) * 0.15 +10000 * 0.10;
            }
            else if(income >= 5001)
            {
                tax = (income - 5000) * 0.10;
            }
            else if(income >= 0)
            {
                tax = 0;
            }
            else
            {
                cout << "Enter negative number, exiting soon..." << endl;
                break;
            }
            cout << "your should pay tax : " << tax << " tvarps." << endl;
            cout << "Please enter another income(if you enter negative number or non-numberic, it will exit.) : ";
        }
        cout << "Exited, Bye !" << endl;
        return 0;
    }

6.编写一个程序，记录捐助给"维护合法权利团体"的资金。该程序要求用户输入捐赠者数目，然后要求用户输入每一个捐献者的姓名和款项。这些信息被存储在一个动态分配的结构数组中.每个数据结构有两个成员：用来存储姓名的字符串数组（或字符串对象）和用来存储款项的double成员。读取所有的数据后,程序将显示所有捐款超过10000的捐款着姓名及其捐款数额。该列表前应包含一个标题，指出下面的捐款者是重要捐款人（Grand Patrons）。然后，程序将列出其他的捐款者，该列表要以Partons开头。如果某种类别没有捐款者，则程序将打印单词“none”。该程序只显示这两种类别，而不进行排序。

代码实现：

#include<iostream>
    #include<string>
    
    using namespace std;
    
    struct DonationInfo{
        string name;
        double amount;
    };
    
    void donationInfoDisplay(DonationInfo donationInfo[], int num, bool isGrandPatrons)
    {
        int countNum = 0;
        for(int i = 0 ; i < num ; i++)
        {
            if(isGrandPatrons)
            {
                if(donationInfo[i].amount > 10000)
                {
                    countNum++;
                    cout << donationInfo[i].name  << endl;
                }
            }
            else
            {
                if(donationInfo[i].amount <= 10000)
                {
                    countNum++;
                    cout << donationInfo[i].name  << endl;
                }
            }
        }
        if(countNum == 0)
            cout << "none" << endl;
    }
    
    int main()
    {
        cout << "Please enter the number of donors :";
        int num;
        while(!(cin >> num))
        {
            cin.clear();
            cin.sync();
            cin.ignore();
            cout << "***[WARNING]:Please enter positive integer.***" << endl;
            cout << "Please enter the number of donors :";
        }
        DonationInfo* donationInfo = new DonationInfo[num];
        for(int i = 0; i < num; i++)
        {
            cout << "enter the donor name :";
            cin >> donationInfo[i].name;
            cout << "enter the donation amount :";
            cin >> donationInfo[i].amount;
        }
        cout << "******Grand Partons******" << endl;
        donationInfoDisplay(donationInfo, num, true);
        cout << "******Partons******" << endl;
        donationInfoDisplay(donationInfo, num, false);
        return 0;
    }

7.编写一个程序,它每次读取一个单词，直到用户只输入q。然后,该程序指出有多少个单词以元音打头，有多少个单词以辅音打头，还有多少个单词不属于这两类。为此，方法之一是，使用isalpha（）来区分以字母和其他字母打头的单词，然后对于通过isalpha（）测试的单词，使用if或switch语句来确定哪些以元音打头。该程序的运行情况如下：

`Enter words (q to quit):`  
`The 12 awesome oxem ambled`  
`quiety across 15 meters of lawn. q`  
`5 words beginning with vowels`  
`4 words beginning with consonants`  
`2 others`

代码实现：

#include<iostream>
    #include<string>
    using namespace std;
    
    int main()
    {
        cout << "Enter words (q to quit) :" << endl;
        string word;
        int vowelNum = 0;
        int consonantNum = 0;
        int othersNum = 0;
        while(cin >> word)
        {
            if(word == "q")
            {
                break;
            }
            else
            {
                if(isalpha(word[0]))
                {
                    switch(word[0])
                    {
                        case 'a':
                        case 'e':
                        case 'i':
                        case 'o':
                        case 'u':
                        case 'A':
                        case 'E':
                        case 'I':
                        case 'O':
                        case 'U':
                            vowelNum++;
                            break;
                        default:
                            consonantNum++;
                    }
                }
                else
                {
                    othersNum++;
                }
            }
        }
        cout << vowelNum << " words beginning with vowels" << endl;
        cout << consonantNum << " words beginning with consonants" << endl;
        cout << othersNum << " others" <<endl;
        return 0;
    }

8.编写一个程序，他打开一个文件，逐个字地读取该文件，直到到达文件末尾，然后指出该文件中包含多少个字符。

代码实现：

#include<iostream>
    #include<fstream>
    
    using namespace std;
    
    int main()
    {
        ifstream txtSource;
        txtSource.open("test.txt", ios::in);
        if(!txtSource.is_open())
        {
            cout << "File failed to open !" << endl;
            exit(EXIT_FAILURE);
        }
        char ch;
        int characterNum = 0;
        while(txtSource >> ch)
        {
            characterNum++;
        }
        cout << "The file contains " << characterNum << " characters" << endl;
        return 0;
    }

9.完成编程练习6，但从文件中读取所需的信息。该文件的第一项应为捐款人数，余下的内容应为对的行。在每一对中，第一行为捐款人姓名，第二行为捐款数额。即该文件类似于下面：

代码实现：

#include<iostream>
    #include<string>
    #include<fstream>
    
    using namespace std;
    
    struct DonationInfo{
        string name;
        double amount;
    };
    
    void donationInfoDisplay(DonationInfo donationInfo[], int num, bool isGrandPatrons)
    {
        int countNum = 0;
        for(int i = 0 ; i < num ; i++)
        {
            if(isGrandPatrons)
            {
                if(donationInfo[i].amount > 10000)
                {
                    countNum++;
                    cout << donationInfo[i].name  << endl;
                }
            }
            else
            {
                if(donationInfo[i].amount <= 10000)
                {
                    countNum++;
                    cout << donationInfo[i].name  << endl;
                }
            }
        }
        if(countNum == 0)
            cout << "none" << endl;
    }
    
    int main()
    {
        cout << "Read file content..." << endl;
        ifstream txtDonationInfo;
        txtDonationInfo.open("test.txt", ios::in);
        if(!txtDonationInfo.is_open())
        {
            cout << "File failed to open !" << endl;
            exit(EXIT_FAILURE);
        }
        int num = 0;
        (txtDonationInfo >> num).get();
        DonationInfo* donationInfo = new DonationInfo[num];
        for(int i = 0; i < num; i++)
        {
            txtDonationInfo >> donationInfo[i].name;
            txtDonationInfo >> donationInfo[i].amount;
        }
        cout << "******Grand Partons******" << endl;
        donationInfoDisplay(donationInfo, num, true);
        cout << "******Partons******" << endl;
        donationInfoDisplay(donationInfo, num, false);
        return 0;
    }

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