int main()
 {Student stud1(1001,"Wang",18,"123 Beijing Road,Shanghua");
  stud1.show_data();
  student2::Student stud2(1102,"Li",'f',89.5);
  stud2.show_data();
  return 0;
 }

 
************************************
//header1.h
#include <string>
namespace student1
 {class Student
    {public:
      Student(int n,string nam,int a,string addr)
       {num=n;name=nam;age=a;address=addr;}
      void show_data();
     private:
      int num;
      string name;
      int age;
      string address;
    };
  void Student::show_data()
    {cout<<"num:"<<num<<"  name:"<<name<<"  age:"<<age
         <<"  address:"<<address<<endl;
    }
 }
   
******************************************
//header2.h
#include <string>
namespace student2
 {class Student
   {public:
     Student(int n,string nam,char s,float sco)
       {num=n;name=nam;sex=s;score=sco;}
     void show_data();
    private:
     int num;
     string name;
     char sex;
     float score;
   };
  
  void Student::show_data()
   {cout<<"num:"<<num<<"  name:"<<name<<" sex:"<<sex
        <<"   score:"<<score<<endl; }
 }

double q(double a,double b,double c)
 {double disc;
  disc=b*b-4*a*c;
  if (disc<0) throw disc;
  return sqrt(disc)/(2*a);
 }
 

struct student
{int num;
 char name[20];
 double score;
};
int main()
{student stud[3]={1001,"Li",78,1002,"Wang",89.5,1004,"Fun",90},stud1[3];
 char c[50];
 int i;
 ostrstream strout(c,50);
 for(i=0;i<3;i++)
  strout<<stud[i].num<<" "<<stud[i].name<<" "<<stud[i].score<<" ";
 strout<<ends;
 cout<<"array c:"<<endl<<c<<endl<<endl;
 istrstream strin(c,50);
 for(i=0;i<3;i++)
  strin>>stud1[i].num>>stud1[i].name>>stud1[i].score;
 cout<<"data from array c to array stud1:"<<endl;
 for(i=0;i<3;i++)
  cout<<stud1[i].num<<" "<<stud1[i].name<<" "<<stud1[i].score<<endl;
 cout<<endl;
 return 0;
}


以下代码可以改一下，改为只建立一个输入输出串流，既用它向字符数组C数据，又从字符数组C读数据。程序如下：
#include <iostream>
#include <strstream>
using namespace std;
struct student
{int num;
 char name[20];
 double score;
};
int main()
{int i;
 student stud[3]={1001,"Li",78,1002,"Wang",89.5,1004,"Fun",90},stud1[3];
 char c[50];
 strstream strio(c,50,ios::in|ios::out);
 for(i=0;i<3;i++)
  strio<<stud[i].num<<" "<<stud[i].name<<" "<<stud[i].score<<" ";
 strio<<ends;
 cout<<"array c:"<<endl<<c<<endl<<endl;
 for(i=0;i<3;i++)
  strio>>stud1[i].num>>stud1[i].name>>stud1[i].score;
 cout<<"data from array c to array stud1:"<<endl;
 for(i=0;i<3;i++)
  cout<<stud1[i].num<<" "<<stud1[i].name<<" "<<stud1[i].score<<endl;
 cout<<endl;
 return 0;
}

void fun1()
{int a[10];
 ofstream outfile1("f1.dat"),outfile2("f2.dat");  //分别定义两个文件流对象
 if(!outfile1)                        //检查打开f1.dat是否成功
  {cerr<<"open f1.dat error!"<<endl;
   exit(1);
  }
 if(!outfile2)                        //检查打开f2.dat是否成功
  {cerr<<"open f2.dat error!"<<endl;
   exit(1);
  }
 cout<<"enter 10 integer numbers:"<<endl;
 for(int i=0;i<10;i++)          //输入10个数存放到f1.dat文件中
  {cin>>a[i];
   outfile1<<a[i]<<" ";}
  cout<<"enter 10 integer numbers:"<<endl;
 for(i=0;i<10;i++)           //输入10个数存放到f2.dat文件中
  {cin>>a[i];
   outfile2<<a[i]<<" ";}
 outfile1.close();               //关闭f1.dat文件
 outfile2.close();               //关闭f2.dat文件
}

//从f1,dat读入10个数，然后存放到f2.dat文件原有数据的后面
void fun2()
{ifstream infile("f1.dat");       //f1.dat作为输入文件
 if(!infile)
  {cerr<<"open f1.dat error!"<<endl;
   exit(1);
  }
  ofstream outfile("f2.dat",ios::app);
 //f2.dat作为输出文件，文件指针指向文件尾，向它写入的数据放在原来数据的后面
  if(!outfile)
   {cerr<<"open f2.dat error!"<<endl;
   exit(1);
  }
  int a;
  for(int i=0;i<10;i++)
   {infile>>a;           //磁盘文件f2.dat读入一个整数
    outfile<<a<<" ";     //将该数存放到f2.dat中
   }
  infile.close();
  outfile.close();
 }

//从f2.dat中读入20个整数，将它们按从小到大的顺序存放到f2.dat
void fun3()
{ifstream infile("f2.dat"); //定义输入文件流infile，以输入方式打开f2.dat
 if(!infile)
  {cerr<<"open f2.dat error!"<<endl;
   exit(1);
  }
 int a[20];
 int i,j,t;
 for(i=0;i<20;i++)     
  infile>>a[i];        //从磁盘文件f2.dat读入20个数放在数组a中
 for(i=0;i<19;i++)     //用起泡法对20个数排序
   for(j=0;j<19-i;j++)
      if(a[j]>a[j+1])
        {t=a[j];a[j]=a[j+1];a[j+1]=t;}
  infile.close();                //关闭输入文件f2.dat
  ofstream outfile("f2.dat",ios::out);
// f2.dat作为输出文件，文件中原有内容删除
  if(!outfile)
   {cerr<<"open f2.dat error!"<<endl;
    exit(1);}
cout<<"data in f2.dat:"<<endl;
  for( i=0;i<20;i++)
    {outfile<<a[i]<<" ";      //向f2.dat输出已排序的20个数
     cout<<a[i]<<" ";}        //同时输出到显示器
  cout<<endl;
  outfile.close();
}

int main()
{fun1();                     //分别调用3个函数
 fun2();
 fun3();
 return 0;
}

int main()
{float a[5];
 cout<<"input data:";
 for(int i=0;i<5;i++)
  cin>>a[i];
 cout<<setiosflags(ios::fixed)<<setprecision(2);
 for(i=0;i<5;i++)
  cout<<setw(10)<<a[i]<<endl;
 return 0;
}

2，用流成员函数控制输出格式
#include <iostream>
using namespace std;
int main()
{float a[5];
 int i;
 cout<<"input data:";
 for(i=0;i<5;i++)
  cin>>a[i];
 cout.setf(ios::fixed);
 cout.precision(2);
 for(i=0;i<5;i++)
  {cout.width(10);
   cout<<a[i]<<endl;}
 return 0;
}

形成三角形的条件是：a+b>c,b+c>a,c+a>b
编写程序，输入a,b,c，检查a,b,c是否满足以上条件，如不满足，由cerr输出有关出错信息。

以下是此题的【c源代码】

#include <iostream>
#include <cmath>
using namespace std;
int main()
{double a,b,c,s,area;
 cout<<"please input a,b,c:";
 cin>>a>>b>>c;
 if (a+b<=c)
  cerr<<"a+b<=c,error!"<<endl;
 else if(b+c<=a)
  cerr<<"b+c<=a,error!"<<endl;
 else if (c+a<=b)
  cerr<<"c+a<=b,error!"<<endl;
 else
  {s=(a+b+c)/2;
   area=sqrt(s*(s-a)*(s-b)*(s-c));
   cout<<"area="<<area<<endl;}
 return 0;
}

上面的C源代码，可以改下，编写计算三角形面积的函数。代码如下：

#include <iostream>
#include <cmath>
using namespace std;

void input(double a,double b,double c)
{cout<<"please input a,b,c:";
 cin>>a>>b>>c;
}
void area(double a,double b,double c)
{double s,area;
 if (a+b<=c)
  cerr<<"a+b<=c,error!"<<endl;
 else if(b+c<=a)
  cerr<<"b+c<=a,error!"<<endl;
 else if (c+a<=b)
  cerr<<"c+a<=b,error!"<<endl;
 else
  {s=(a+b+c)/2;
   area=sqrt(s*(s-a)*(s-b)*(s-c));
   cout<<"area="<<area<<endl;}
}
int main()
{double a=2,b=3,c=5;
 input(a,b,c);
 area(a,b,c);
 return 0;
}
 

//定义Circle(圆形)类
class Circle:public Shape
{public:
Circle(double r):radius(r){}                                     //结构函数
  virtual double area() const {return 3.14159*radius*radius;};   //定义虚函数
 protected:
  double radius;                                                 //半径
};

//定义Square(正方形)类
class Square:public Shape
{public:
  Square(double s):side(s){}                                     //结构函数    
  virtual double area() const {return side*side;}                //定义虚函数
 protected:
  double side;
};

//定义Rectangle(矩形)类
class Rectangle:public Shape
{public:
 Rectangle(double w,double h):width(w),height(h){}               //结构函数
 virtual double area() const {return width*height;}              //定义虚函数
 protected:
  double width,height;                                           //宽与高
};

//定义Trapezoid(梯形)类
class Trapezoid:public Shape
{public:
  Trapezoid(double t,double b,double h):top(t),bottom(t),height(h){} //结构函数
  virtual double area() const {return 0.5*(top+bottom)*height;}      //定义虚函数
 protected:
  double top,bottom,height;                                          //上底、下底与高
};

//定义Triangle(三角形)类
class Triangle:public Shape
{public:
  Triangle(double w,double h):width(w),height(h){}                //结构函数
  virtual double area() const {return 0.5*width*height;}          //定义虚函数
 protected:
  double width,height;                                            //宽与高
};

int main()
{
 Circle circle(12.6);                                             //建立Circle类对象circle
 Square square(3.5);                                              //建立Square类对象square
 Rectangle rectangle(4.5,8.4);                                    //建立Rectangle类对象rectangle
 Trapezoid trapezoid(2.0,4.5,3.2);                                //建立Trapezoid类对象trapezoid
 Triangle triangle(4.5,8.4);                                      //建立Triangle类对象
 Shape *pt[5]={&circle,&square,&rectangle,&trapezoid,&triangle}; 
                                              //定义基类指针数组pt，使它每一个元素指向一个派生类对象
 double areas=0.0;                                                //areas为总面积
 for(int i=0;i<5;i++)
  {areas=areas+pt[i]->area();}
 cout<<"totol of all areas="<<areas<<endl;   //输出总面积
 return 0;
}

//定义Circle类
class Circle:public Shape
{public:
Circle(double r):radius(r){}                                     //结构函数
  virtual double area() const {return 3.14159*radius*radius;};   //定义虚函数
 protected:
  double radius;                                                 //半径
};

//定义Rectangle类
class Rectangle:public Shape
{public:
 Rectangle(double w,double h):width(w),height(h){}               //结构函数
 virtual double area() const {return width*height;}              //定义虚函数
 protected:
  double width,height;                                           //宽与高
};

class Triangle:public Shape
{public:
  Triangle(double w,double h):width(w),height(h){}                //结构函数
  virtual double area() const {return 0.5*width*height;}          //定义虚函数
 protected:
  double width,height;                                            //宽与高
};

//输出面积的函数
void printArea(const Shape &s)
{cout<<s.area()<<endl;}                                            //输出s的面积

int main()
{
 Circle circle(12.6);                                             //建立Circle类对象circle
 cout<<"area of circle    =";         
 printArea(circle);                                               //输出circle的面积
 Rectangle rectangle(4.5,8.4);                                    //建立Rectangle类对象rectangle
 cout<<"area of rectangle =";                                    
 printArea(rectangle);                                            //输出rectangle的面积
 Triangle triangle(4.5,8.4);                                      //建立Triangle类对象
 cout<<"area of triangle  =";
 printArea(triangle);           //输出triangle的面积
 return 0;
}