C++ Primer Plus笔记: 2023.07.17

1.不接受任何参数的cin.get( )成员函数返回输入中的下一个字符，也就是说，可以这样使用它：

ch = cin.get() ;

该函数的工作方式与C语言中的getchar( )相似，将字符编码作为int值返回；而cin.get(ch)返回一个对象，而不是读取的字符。

2.当要写条件表达式时：

if (myNumber == 3)

有些程序员为了以防万一自己出现这样的错误：

if (myNumber = 3)

这种错误编译器回报出警告，为了能让编译器直接报错以便自己能更容易发现，干脆这么写：

if (3 == myNumber) 

3.下面这种情况：

int n ;
cin >> n ;

如果用户输入一个单词，而不是一个数字。将发生4种情况：
（1）n的值保持不变
（2）不匹配的输入将被留在输入队列中
（3）cin对象中的一个错误标记被设置
（4）对cin方法的调用将返回false （如果被转换为bool类型）

第六章编程题：
（1）

#include 
#include 
using namespace std ;

char ch ;

int main()
{
	while ((ch = cin.get()) != '@')
	{
		if (!(ch >= '0' && ch <= '9'))
		{
			if (ch >= 'A' && ch <= 'Z')
			{ 
				cout << char(tolower(ch)) ;
				continue ;
			}
			else if (ch >= 'a' && ch <= 'z') 
			{
				cout << char(toupper(ch)) ;
				continue ;
			}
			cout << ch ;
		}
	}
}

(2)
第一种解法：

#include 
using namespace std ;

const int ArSize = 10 ;
	
int main()
{
	double array[ArSize] = {0} ;
	double donation, sum = 0 ;
	int count = 0 ;
	
	while (count < ArSize && cin >> donation)
	{
		array[count ++] = donation ;
		sum += donation ;
	}
	
	cout << "The Averge = " << sum / count << endl ;
	
	int more = 0 ;
	double average = sum / count ;
	for (int i = 0; i < count; i++)
		if (array[i] > average) more ++ ;
	
	cout << more << " members beyond the average.\n" ;
}

第二种解法：

#include 
#include 
using namespace std ;

const int ArSize = 10 ;

int main()
{
	array<double, ArSize> array ;
	double donation ;
	double average, sum = 0 ;
	int count = 0 ;

	while (count < ArSize && cin >> donation)
	{
		array[count++] = donation ;
		sum += donation ;
	}

	average = sum / count ;
	cout << "The average = " << average << endl ;
	
	int more = 0 ;
	for (int i=0; i<count; i++)
		if (array[i] > average) more++ ;
	
	cout << more << " numbers beyond the average.\n" ;
	return 0 ;
}

(3)

#include 
using namespace std ;

void showmenu() ;

int main()
{
	showmenu() ;
	char ch ;
	while(cin >> ch && ch != '@')
	{
		switch (ch)
		{
			case 'c' :
			case 'C' : cout << "A maple is a carnivore.\n" ;
				       break ;
			case 'p' :
            case 'P' : cout << "A maple is a pianist.\n" ;
                       break ;
			case 't' :
            case 'T' : cout << "A maple is a tree.\n" ;
                       break ;
			case 'g' :
            case 'G' : cout << "A maple is a game.\n" ;
					   break ;
			default : cout << "Please enter a c, p, t, or g: " ;
				      continue ;
		}
		showmenu() ;
	}
}

void showmenu()
{
	cout << "Please enter one of the following choices:\n"
		"c) carnivore		p) pianist\n"
		"t) tree           	g) game\n" ;
}

(4)

#include 
using namespace std ;

const int strsize = 50 ;
struct bop {
	char fullname[strsize] ;
	char title[strsize] ;
	char bopname[strsize] ;
	int preference ; 
} ;
const int Members = 5 ;

void showmenu() ;
void Print_by_name(bop * bopmembers) ;
void Print_by_title(bop * bopmembers) ;
void Print_by_bopname(bop * bopmembers) ;
void Print_by_preference(bop * bopmembers) ;

int main()
{
	bop bopmembers[Members] = {
		{
			"Wimp Macho" ,
			"Java programmer" ,
			"ooop" ,
			0
		} ,
		{
			"Raki Rhodes" ,
			"Junior Programmer" ,
			"uiwieqw" ,
			1
         } ,
		 {
			"Celia Laiter" ,
			"C programmer" ,
			"MIPS" ,
			2
		 } ,
		 {
			"Hoppy Hipman" ,
			"Analyst Trainee" ,
			"rtrer" ,
			1
		 } ,
		 {
			"Pat Hand" ,
            "PHP programmer" ,
            "LOOPY" ,
            2
         } 
	} ;
	
	char choice ;
	showmenu() ;
	cout << "Enter your choice: " ;
	while (cin >> choice)
	{
		switch (choice)
		{
			case 'a' :
			case 'A' : Print_by_name(bopmembers) ;
				   	   break ;
			case 'b' :
            case 'B' : Print_by_title(bopmembers) ;
                       break ;
			case 'c' :
            case 'C' : Print_by_bopname(bopmembers) ;
                       break ;
			case 'd' :
	        case 'D' : Print_by_preference(bopmembers) ;
                       break ;
			case 'q' :
			case 'Q' : goto END ;
			default	 : goto NEXT ; 
		}
		NEXT : cout << "Next choice: " ;
	}
	
	END : cout << "Bye!\n" ;
}

void showmenu()
{
	cout << "Benevolent Order of Programmers Report\n"
		    "a. display by name	b. display by title\n"
		    "c. display by bopname	d. display by preference\n"
		    "q. quit\n" ;
}

void Print_by_name(bop * bopmembers)
{
	for (int i=0; i<Members; i++)
		cout << bopmembers[i].fullname << endl ;
}

void Print_by_title(bop * bopmembers)
{
	for (int i=0; i<Members; i++)
		cout << bopmembers[i].title << endl ;
}

void Print_by_bopname(bop * bopmembers)
{
	for (int i=0; i<Members; i++)
		cout << bopmembers[i].bopname << endl ;
}

void Print_by_preference(bop * bopmembers)
{
	for (int i=0; i<Members; i++)
	{
		if (bopmembers[i].preference == 0)
			cout << bopmembers[i].fullname << endl ;
		else if (bopmembers[i].preference == 1)
			cout << bopmembers[i].title << endl ;
		else if (bopmembers[i].preference == 2)
			cout << bopmembers[i].bopname << endl ;
	}
}

(5)

#include 
using namespace std ;

void Calculate (double income) ;

int main()
{
	double income ;
	double sum = 0 ;
	cout << "Please enter you income: " ;
	while(cin >> income)
	{
		if (income < 0) break ;
		Calculate (income) ;
		sum = 0 ;
		cout << "Please enter you income: " ;
	}
	cout << "Done." << endl ;
	return 0 ;
}

void Calculate (double income)
{
	double sum = 0 ;
	if (income <= 5000 ) 
		sum += income * 0.00 ;
	else {
		sum += 5000 * 0.00 ;
		income -= 5000 ;
		if (income <= 10000) sum += income * 0.10 ;
		else
		{
			sum += 10000 * 0.10 ;
			income -= 10000 ;
			if (income <= 20000) sum += income * 0.15 ;
			else
			{
				sum += 20000 * 0.15 ;
				income -= 20000 ;
				sum += income * 0.20 ;
			}
		}
	}
	cout << "Your income tax = " << sum << " tvarps." << endl ;
}

(6)

#include 
using namespace std ;

const int NameSize = 30 ;
struct Contributor
{
	char name[NameSize] ;
	double money ;
} ;
int population ;

int main()
{
	cout << "How many people contirbute: " ;
	cin >> population ;
	cin.get() ;
	Contributor * volunteer = new Contributor[population] ;
	
	cout << "Enter their name and money:\n" ;
	for (int i=0; i<population; i++)
	{
		cin.get(volunteer[i].name, NameSize).get() ;
		cin >> volunteer[i].money ;
		cin.get() ;
	}
	
	cout << "Grand Patrons:\n" ;
	for (int i=0; i<population; i++)
	{
		if (volunteer[i].money > 10000)
		{
			cout << volunteer[i].name << " "
			     << volunteer[i].money << endl ;
			volunteer[i].money = 0 ;
		}
	}

	cout << "Patrons:\n" ;
    for (int i=0; i<population; i++)
		if (volunteer[i].money )
			cout << volunteer[i].name << " "
                 << volunteer[i].money << endl ;
	
	delete [] volunteer ;
}

(7）

#include 
#include 
#include 
using namespace std ;

string vocabulary ;

int main()
{
	int vowels = 0, consonants = 0, other = 0 ;
	cout << "Enter words (q to quit):\n" ;
	while (cin >> vocabulary && vocabulary != "q")
	{
		if( !isalpha(vocabulary[0]) ) 
		{
			other++ ;
			continue ;
		}
		switch(vocabulary[0])
		{
			case 'A' :
            case 'E' :
            case 'I' : 
            case 'O' :
			case 'a' :
			case 'e' :
			case 'i' :
			case 'o' : vowels ++ ; break ;
			default  : consonants ++ ; break ;
		}
	}

	cout << vowels << " words beginning with vowels\n" ;
	cout << consonants << " words beginning with consonants\n" ;
	cout << other << " others\n" ;
}