下面不能够判断字符串S是空串的是(　　)

声明复数类Complex，该类中有两个私有变量rel，image分别表示一个复数的实部和虚部。为Complex类添加适当的构造函数，并使用友元函数add实现复数加法。

#include ﹤iostream﹥

using namespace std;

class Complex

{

private:

double real, image;

public:

void setRI( double a, double b)

{

real=a;image=b;

}

double getReal( )

{

return real;

}

double getImage( )

{

return image;

}

void print( )

 {

if( image ﹥0)

cout﹤﹤"复数:"﹤reall﹤﹤"+"﹤﹤ image﹤﹤"i"﹤﹤endl;

if( image ﹤0)

cout﹤﹤"复数:"﹤﹤real﹤﹤"-"﹤﹤ image﹤﹤"i﹤endl;

}

friend Complex add( Complex, Complex); //声明友元函数

};

void main( )

{

Complex c1(19, 0.864), c2, c3;

c2.setRI(90,125.012);

c3=add(c1, c2)cout﹤﹤"复数一:";

c1.pint( );cout﹤﹤"复数二:";

c2.pint( );cout﹤﹤"相加后:";

 c3.pint( );

}

#include ﹤iostream. h﹥

class Based

{public:

Based( )

{cout﹤﹤" Based构造函数\n"; fun( ); }

virtual void fun( )

{cout﹤﹤" Based::fun( )函数\n"; }

};

class Derived: publicBase

{public:

Derived( )

{cout﹤﹤" Derived构造函数\n"; fun( ); }

void fun( )

 { cout﹤﹤"Derived::fun( )函数\n"; }

};

void main( )

{Derived d;}

下面是一个输入半径，输出其面积和周长的C++程序，在横线处填上正确的语句。(圆周率为3.14159)#include "stdafx. h"

#include ﹤iostream﹥

#include "math. h"

using namespace std;

_________ //宏定义void main( )

{

double rad;

cout ﹤﹤ "rad =";cin ﹥﹥ rad;

double l=2.0*pi *rad;_________;

cout﹤﹤ "\n The long is: "﹤﹤l﹤﹤ endl;

cout﹤﹤ "The area is: "﹤﹤s﹤﹤ endl;

}

#include ﹤iostream. h﹥

class example

{

int a;public:example(int b=5)

{ a=b++; }

void print( )

{ a=a+1; cout﹤﹤a﹤﹤" "; }

void print( )

const

{ cout ﹤﹤a﹤﹤ endl; }

};

void main( )

{ example x;const example y(2);x. print( );y. print( );}

在下面程序的横线处填上适当的字句，使输出为：0,2,10。

#include "stdafx. h"

#include ﹤iostream﹥

#include "math. h"

using namespace std;

class Magic

{

 double x;

public:

Magic( double d =0. 00): x( fabs(d))

{ }

Magic operator +(_________){return Magic(sqrt(x*x+c. x*c. x));

}

_________&operator ﹤﹤(ostream & stream, Magic &c)

{ stream ﹤﹤c.x;return stream;}

};

void main( )

{

Magic ma;

cout ﹤﹤ma﹤﹤","﹤﹤Magic(2)﹤﹤", "﹤﹤ma+Magic(-6)+ Magic(-8)﹤﹤endl;

}

在下面程序的横线处填上适当的字句，使该程序执行结果为40。

#include ﹤iostream.h﹥

class Test

{

public:_________;

Test (int i=0)

{ x=i+x; }

int Geytnum( )

{ return Test:: x +10; }

};

_________;

void main( )

{

Test test;cout ﹤﹤ test. Getmum( )﹤﹤ endl;

}

在下面程序的横线处填上适当字句，完成类的定义。

class line;

class box

{

private:

int color;

int upx, upy;

int lowx, lowy;

pubnic:

_________void set_color (int c )

{

 color =c;

}void define_box(int x1, int y1, int x2, int y2)

{ upx=x1; upy =y1; lowx =x2; lowy =y2; }

};

class line

{

private:

int color;

int startx, starty;

int endx, endy;

public:

friend int same_color(line l, box b)

void set_color (int c) { color =c; }

void define_line(_________)

{ startx =x1; starty =y1; endx =x2; endy =y2; }

};

int same_color (line l, box b)

{

 if (l. color==b. color) return l;

retum 0;

}

1 #include ﹤iostream﹥

2 using namespace std;

3 int main( )

4 { inta=10, b=18, c=77;

5 const int *p = c;

6 cout ﹤﹤*p﹤﹤ endl;

7 return 0;

8 }

下面程序中用来求数组和。请在下面程序的横线处填上适当内容，以使程序完整，并使程序的输出为：s=150。

#include ﹤iostream.h﹥

class Arr

{

int *a, n;

public:

Arr( ):a(0),n(0) { }Arr( int *aa, int nn)

{

n=nn;a= new int[n];

for(int i=0; i﹤nn; i ++)*(a+i)=*(aa+i);

}

~Arr( )

{delete a; }

_________;

{

return *(a+i);

}

};

void main( )

{

int b[5]={10,20,30,40,50};

Arr a1(b, 5)int i=0, s=0;

_________s+=a1. GetValue(i);

cout﹤﹤"s="﹤﹤s﹤﹤endl;

}

1 #include ﹤iostream﹥

2 using namespace std;

3 int main( ){

4 const int num =20;

5 int scores[num];

6 for(int i=1; i﹤=num; i ++)

7 scores[i]=i;

8 return 0; }