《C++编程思想》（第二版）第2章 对象的创建和使用（习题及答案）

与习题相关的代码Hello.cpp

<span style="font-size:18px;">#include <iostream>
using namespace std;

int main()
{
cout << "Hello, World! I am "
<< 8 << " Today!" << endl;
}</span>

Stream2.cpp[/code]

<span style="font-size:18px;">#include <iostream>
using namespace std;

int main()
{
cout<<"a number in decimal:"
<<dec<<15<<endl;
cout<<"in octal:"<<oct<<15<<endl;
cout<<"in hex:"<<hex<<15<<endl;
cout<<"a floatint-point number:"
<<3.14159<<endl;
cout<<"non-printing char (escape):"
<<char(27)<<endl;
return 0;
}</span>

[/code]

Nomconv.cpp

<span style="font-size:18px;">#include <iostream>
using namespace std;

int main()
{
int number;
cout<<"Enter a decimal number:";
cin>>number;
cout<<"value in octal = 0"
<<oct<<number<<endl;
cout<<"value in hex = 0x"
<<hex<<number<<endl;
return 0;
}</span>

[/code]

Fillvector.cpp

<span style="font-size:18px;">#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

int main()
{
vector<string> v;
ifstream in("Fillvector.cpp");
string line;
while(getline(in,line))
{
v.push_back(line);
}
for(int i = 0;i < v.size();++i)
{
cout<<i<<":"<<v[i]<<endl;
}
return 0;
}</span>

2-1修改Hello.cpp，使他打印你的名字和年龄（或者你的鞋码、爱犬的年龄等，只要你喜欢）。编译并运行修改后的程序。[/code]

<span style="font-size:18px;">#include <iostream>
using namespace std;

int main()
{
cout << "Hello, World! I am ZY." << endl;
cout << "I am 19 years:" << endl;
return 0;
}</span>

2-2以Stream.cpp、Numconv.cpp为例，编一个程序，让它根据输入的半径值求出圆面积并打印。可以用运算符“*”求直径的平方。注意，不要用八进制或十六进制格式打印（它们只适用整数类型）。[/code]

#include <iostream>
using namespace std;

int main()
{
const float pi = 3.141592654;
cout << "Enter the radius: ";

float radius;
cin >> radius;
cout << "The area is " << pi * radius * radius << endl;

return 0;
}

[/code]

2-3编一个程序用来打开文件并统计文件中以空格隔开的单词数目。

#include <string>
#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main()
{
ifstream f("test.cpp");
int nwords = 0;
string word;

while (f >> word)
{
++nwords;
}

cout << "Number of words = " << nwords << endl;

return 0;
}

[/code]

2-4编一个程序统计文件中特定单词出现的次数（要求使用string类的运算符“==”来查找单词）。

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

int main(int argc, char* argv[])
{
// Process command-line arguments:
if (argc < 3)
{
cerr << "usage: WordCount word file\n";
return -1;
}
string word(argv[1]);
ifstream file(argv[2]);

// Count occurrences:
long wcount = 0;
string token;
while (file >> token)
if (word == token)
++wcount;

// Print result:
cout << '"' << word << "\" appeared "
<< wcount << " times\n";
}

[/code]

2-5修改Fillvector.cpp是他从后向前打印各行。

方法一：

#include <string>
#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

int main()
{
vector<string> v;
ifstream in("Fillvector.cpp");
string line;
while(getline(in, line))
{
v.push_back(line);
}

// Print backwards:
for(int i = v.size()-1; i > 0; --i)
{
cout << v.size()-1 << ": " << v[i] << endl;
}
return 0;
}

方法二：[/code]

#include <string>
#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

int main()
{
vector<string> v;
ifstream in("Fillvector.cpp"<span style="font-family: Arial, Helvetica, sans-serif;">);</span>
string line;
while(getline(in, line))
v.push_back(line);

// Print backwards:
int nlines = v.size();
for(int i = 0; i < nlines; i++)
{
int lineno = nlines-i-1;
cout << lineno << ": " << v[lineno] << endl;
}
return 0;
}

[/code]

2-6修改Fillvector.cpp使他把vector中的所有元素连接成单独的一个字符串，并打印，但不要加上行号。

#include <string>
#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

int main()
{
vector<string> v;
ifstream in("Fillvector.cpp");
string line;
while(getline(in, line))
{
v.push_back(line);
}
// Put lines into a single string:
string lines;
for(int i = 0; i < v.size(); i++)
{
lines += v[i] + "\n";
}
cout << lines;
return 0;
}

[/code]

2-7编一个程序，一次显示文件的一行，然后，等待用户按回车键后显示下一行。

#include <string>
#include <iostream>
#include <fstream>
using namespace std;

int main()
{
ifstream in("test.cpp");
string line;
while(getline(in, line))
{
cout << line;  // No endl!
cin.get();
}

return 0;
}

[/code]

2-8创建一个vector<float>，并用一个for循环语句向它输入25个浮点数，显示vector的结果。

#include <iostream>#include <vector>using namespace std;int main(){// Fill vector:vector<float> v;for (int i = 0; i < 25; ++i){v.push_back(i + 0.5);}// Displayfor (int i = 0; i < v.size(); ++i){cout << v[i]<<" ";}cout << endl;return 0;}

[/code]

2-9创建三个vector<float>对象，与第八题一样填写前两个对象。编一个for循环，把前两个vector的每一个对应的元素相加起来，结果放入第三个vector的相应元素中。显示这三个vector的结果。

方法一：

#include <iostream>#include <vector>using namespace std;int main(){vector<float> v1, v2;for (int i = 0; i < 25; ++i){v1.push_back(i);v2.push_back(i + 0.2);}// Form sum:vector<float> v3;for (int i = 0; i < v1.size(); ++i){v3.push_back(v1[i] + v2[i]);}// Display:for (int i = 0; i < v1.size(); ++i){cout << v1[i] << " + " << v2[i]<< " = " << v3[i] << endl;}return 0;}

方法二：[/code]

#include <iostream>#include <vector>using namespace std;int main(){vector<float> v1, v2;for (int i = 0; i < 25; ++i){v1.push_back(i);v2.push_back(i + 0.2);}// Form sum:vector<float> v3;v3.resize(v1.size());  // pre-allocate spacefor (int i = 0; i < v1.size(); ++i){v3[i] = v1[i] + v2[i];}// Display:for (int i = 0; i < v1.size(); ++i){cout << v1[i] << " + " << v2[i]<< " = " << v3[i] << endl;}return 0;}

[/code]

2-10编一个程序，创建一个vector<float>，像前面的练习那样输入25个数。求每个数的平方，并把它们放入vector的同样位置。显示运算前后的vector。

#include <iostream>#include <vector>using namespace std;int main(){// Fill and print:vector<float> v;for (int i = 0; i < 25; ++i){v.push_back(i);}for (int i = 0; i < v.size(); ++i){cout << v[i]<<" ";}cout<<endl;// Square and print:for (int i = 0; i < v.size(); ++i){v[i] = v[i] * v[i];}for (int i = 0; i < v.size(); ++i){cout << v[i]<<" ";}cout<<endl;return 0;}

[/code]