[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

时间:2021-04-17 05:56:08

程序清单6.2

#include<iostream>
using namespace std; void main() {
char ch;
cout << "Type, and I shall repeat.\n";
cin.get(ch);
while(ch != '.')
{
if (ch == '\n')
cout << ch;
else
cout << ++ch;
cin.get(ch);
}
system("pause");
}

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

程序清单6.5

#include<iostream>
using namespace std; const int Size = ;
void main() {
float naaq[Size];
int i = ;
float temp;
cout << "First value:";
cin >> temp;
while (i < Size&&temp >= ) {
naaq[i] = temp;
++i;
if (i<Size)
{
cout << "Next value:";
cin >> temp;
}
}
if ( == i)
cout << "No data!" << endl;
else {
cout << "Enter your NAAQ:";
float you;
cin >> you;
int count = ;
for (int j = ; j < i; j++)
{
if (naaq[j] > you)
++count;
}
cout << count << "个数字比你的大" << endl;
}
system("pause");
}

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

程序清单6.8(字符函数库cctype)

#include<iostream>
#include<cctype>
using namespace std; void main() {
cout << "Enter text for analysis,and type @ to terminate input."<<endl;
char ch;
int space = , digit = , chars = , punct = , others = ; cin.get(ch);
while (ch!='@')
{
if (isalpha(ch)) chars++;
else if (isspace(ch)) space++;
else if (isdigit(ch)) digit++;
else if (ispunct(ch)) punct++;
else others++;
cin.get(ch);
}
cout << chars << " letters,"
<< space << " whitespace,"
<< digit << " digit,"
<< punct << " punctuations,"
<< others << " others." << endl;
system("pause");
}

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

程序清单6.13

#include<iostream>
using namespace std;
const int Max = ;
void main() {
double fish[Max];
cout << "Enter the weights of your fish.\nYou may enter up to " << Max << " fish<q to terminate>." << endl;
cout << "fish #1: ";
int i = ;
while (i<Max&&cin >> fish[i])
{
if (++i < Max)
cout << "fish #" << i + << ": ";//i+1和++i不同,i+1对i的值没有影响
}
double total = 0.0;
for (int j = ; j < i; j++)//i=5
total += fish[j];
if (i == )
cout << "No fish!" << endl;
else
cout << total / i << "=average weight of " << i << " fish" << endl;
system("pause");
}

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

根据自己的习惯重新编写

#include<iostream>
using namespace std;
const int Max = ;
void main() {
double fish[Max],sum=;
cout << "Enter the weights of your fish.\nYou may enter up to " << Max << " fish<q to terminate>." << endl;
int i;
for (i = ; i < Max; i++)
{
cout << "fish #" << i + << ": ";
if (cin >> fish[i])//输入成功返回true
sum += fish[i];
else
break;
}
if (i == )
cout << "No fish!" << endl;
else
cout << sum/i<< "=average weight of " << i << " fish" << endl;
system("pause");
}

程序清单6.14

#include<iostream>
using namespace std;
const int Max = ;
void main() {
double golf[Max],sum=;
cout << "Enter your golf scores.\nYou must enter " << Max << " rounds." << endl;
int i;
for (i = ; i < Max; i++)
{
cout << "round #" << i + << ": ";
while (!(cin>>golf[i]))
{
cin.clear();
while (cin.get() != '\n')
continue;
cout << "Please enter a number:";
}
sum += golf[i];
}
cout << sum/Max<< "=average score " <<Max<< " rounds" << endl;
system("pause");
}

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

程序清单6.15(文本I/O)

//文件输出(对程序而言)

#include<iostream>
#include<fstream>
using namespace std; void main() {
char automobile[];
int year;
double a_price, d_price; //声明ofstream对象并将其同文件关联起来
ofstream outFile;
outFile.open("first.txt"); cout << "Enter the make and model of automobile:";
cin.getline(automobile, );//cin.getline:不断读取,直到遇到换行符(少于50个字符),在末尾加上一个空字符,换行符被丢弃
cout << "Enter the model year:";
cin >> year;
cout << "Enter the original asking price:";
cin >> a_price;
d_price = 0.913*a_price; cout << fixed;//表示用一般的方式输出浮点数,比如num=0.00001,cout输出为1e-005,加了fixed后再输出就为0.000010
cout.precision();//第一位精确,第二位四舍五入,比如num = 318.15,precision(2)为3.2e+02,precision(4)为318.2
cout.setf(ios_base::showpoint);//强制显示小数点
cout << "Make and model: " << automobile << endl;
cout << "Year: " << year << endl;
cout << "Was asking $" << a_price << endl;
cout << "Now asking $" << d_price << endl; outFile << fixed;
outFile.precision();
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();
system("pause");
}

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

程序清单6.16

//文件读入(对程序而言)

#include<iostream>
#include<fstream>//文件I/O
#include<cstdlib>//exit()
using namespace std;
const int SIZE = ; void main()
{
char filename[SIZE];
ifstream inFile;//声明ifstream对象
cout << "Enter name of data file:";
cin.getline(filename, SIZE);
inFile.open(filename);//关联文件 if (!inFile.is_open())//文件打开失败
{
cout << "Could not open the file " << filename << endl;
exit(EXIT_FAILURE);
}
double value, sum = 0.0;
int count = ; inFile >> value;
while (inFile.good())//输入正确
{
++count;
sum += value;
inFile >> value;
}
if (inFile.eof())
cout << "End of file reached." << endl;
else if (inFile.fail())
cout << "Input terminated by data misamatch." << endl;
else
cout << "Input terminated for unknown reason." << endl;
if (count == )
cout << "No data processed." << endl;
else {
cout << "Items read: " << count << endl;
cout << "Sum: " << sum << endl;
cout << "Average: " << sum / count << endl;
}
inFile.close(); system("pause");
}

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

要想正确运行,首先在源代码文件夹中创建一个包含double数字的文本文件。

为何会少了最后一个数字17.5呢?

[C++ Primer Plus] 第6章、分支语句和逻辑运算符(一)程序清单

在文本文件中,输入最后的文本17.5后应该按下回车键,然后再保存文件。