《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

<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>

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>

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。

<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）。

#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;}

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;}

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";} 

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：

#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;} 

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;} 

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;}

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);  }  // Display  for (int i = 0; i < v.size(); ++i)   {  cout << v[i]<<" ";  }  cout << endl;  return 0;}

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：

#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 space  for (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;}

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;}