C++编程思想第二章课后答案

2.2

//:S02:Area.cpp
#include<iostream>
using namespace std;
int main()
{
const float pi=3.141592654;
float radius;
cout<<"Enter the radius: ";
cin>>radius;
cout<<"The area is "<<pi * radius * radius<<endl;
}
/*Sample Exclusion:
Enter the radius: 10
The area is 314.159
*/
///:~

2.3

//:S02:WordCount.cpp
#include<iostream>
#include<string>
#include<fstream>
using namespace std;
int main()
{
ifstream in("WordCount.cpp");
string s;
int i=0;
while (in>>s)
{
i++;
}
cout<<"Number of words = "<<i<<endl;
}
///:~

2.4

//:S02:WordCount2.cpp
#include<iostream>
#include<string>
#include<fstream>
using namespace std;
int main()
{
ifstream in("WordCount.cpp");
string s;
string equal="word";
int i=0;
while (in>>s)
{
if (s==equal)
{
i++;
}
}
cout<<"the string \""+equal+"\" appeared "<<i<<" times!"<<endl;
}
///:~

2.5

//:S02:FillVector.cpp
#include<iostream>
#include<string>
#include<fstream>
#include<vector>
using namespace std;
int main()
{
ifstream in("FillVector.cpp");
string line;
vector<string>v;
while (getline(in,line))
{
v.push_back(line);
}
int nlines=v.size();
for (int i=0;i<nlines;i++)
{
cout<<nlines-i<<":"<<v[nlines-i-1]<<endl;
}
}
///:~

2.6

//:S02:FillVector.cpp
#include<iostream>
#include<string>
#include<fstream>
#include<vector>
using namespace std;
int main()
{
ifstream in("FillVector2.cpp");
string line,nlines;
vector<string>v;
while (getline(in,line))
{
v.push_back(line);
}
for (int i=0;i<v.size();i++)
{
nlines += v[i]+"\n";
}
cout<<nlines;
}
///:~

2.7
//:S02:FileView.cpp
#include<iostream>
#include<string>
#include<fstream>
using namespace std;
int main()
{
ifstream in("FileView.cpp");
string line;
while (getline(in,line))
{
cout<<line;//没有换行符
cin.get();//用户输入回车键
}
}
///:~

2.8
//:S02:FloatVector.cpp
#include<iostream>
#include<vector>
using namespace std;
int main()
{
vector<float>v;
for (int i=0;i<25;i++)
{
v.push_back(i+0.5);
}
for (i=0;i<v.size();i++)
{
cout<<v[i]<<" ";
}
cout<<endl;
}
///:~

2.9
//:S02:FloatVector2.cpp
#include<iostream>
#include<vector>
using namespace std;
int main()
{
vector<float>v1,v2;
for (int i=0;i<25;i++)
{
v1.push_back(i+0.5);
v2.push_back(25-i-1);
}
vector<float>v3;
for (i=0;i<v1.size();i++)
{
v3.push_back(v1[i]+v2[i]);
}
for (i=0;i<v1.size();i++)
{
cout<<v1[i]<<"+"<<v2[i]<<"="<<v3[i]<<endl;
}
}
///:~

2.10
//:S02:FloatVector3.cpp
#include<iostream>
#include<vector>
using namespace std;
int main()
{
vector<float>v;
for (int i=0;i<25;i++)
{
v.push_back(i);
}
for (i=0;i<v.size();i++)
{
cout<<v[i]<<" ";
}
cout<<endl;
for (i=0;i<v.size();i++)
{
v[i]=v[i]*v[i];
}
for (i=0;i<v.size();i++)
{
cout<<v[i]<<" ";
}
cout<<endl;
}
///:~