通过C++语言中的_________机制，可以从现存类中构建其子类。

在三角形类tri实现两个函数，功能是输入三个顶点坐标判断是否构成等边三角形　　#include ﹤iostream.h﹥

#include ﹤math.h﹥

class point { point

private: float x, y;

public: f(float a, float b){x=a; y=b;}

f( ){x=0; y=0;}

Void set(float a, float b){x=a; y=b;}

float getx( ){return x;}

noat gety( ){return y;}

};

class tri{

point x, y, z;

float s1, s2, s3;

public....settri(....); //用于输入三个顶点坐标

....test(....); //用于判断是否构成等边三角形　　};

请写出两个函数的过程(如果需要形式参数，请给出形参类型和数量，以及返回值类型)

#include ﹤iostream.h﹥

class A

{

public:

A( );

void Show( );

～A( );

private:

static int c;

};

int A:: c=O;

A:: A( )

{

cout﹤﹤"constructor."﹤﹤endl;

c +=10;

}

void A:: Show( )

{

cout﹤﹤"c="﹤﹤c﹤﹤endl;

}

A:: ～A( )

{

cout﹤﹤"destrucator."﹤﹤endl;

}

void main( )

{

A a, b;

a.Show( );

b.Show( );

}

#lnclude ﹤iostream.h﹥

void func( );

void main( )

{

for(int i=0; i﹤6; i++)

{

func( );

}

}

void func( )

{

int x=0;

x++;

static int y=0;

y++;

cout﹤﹤"x="﹤﹤x﹤﹤";y="﹤﹤y﹤﹤endl;

}

求两个浮点数之差的cha函数的原型声明、调用方法。

#include ﹤iostream﹥

using namespace std;

void main( )

{

float a, b;

_________; //函数cha的原型声明

a=12.5;

b=6.5;

float c=_____________; //调用函数cha

cout﹤﹤c﹤﹤endl;

}

float cha(float x,float y)

{

float w;

w=x-y;

return w;

}

下面程序的运行结果如下：

This is line1

This is line2

This is line3

将下列程序补充完整，答案写在答题纸上。源程序如下：

#include ﹤iostream﹥

#include _________

using namespace std;

void main( )

{

fstream fin, fout;

fout.open("my.txt", ios:: out);

if(!fout.is_open( ))

return;

for(int i=0; i﹤3; i=i+1)

fout﹤﹤"This is line"﹤﹤i+1﹤﹤endl;

fout.close( );

fin.open("my.txt", ios:: in);

if(! fin.is_open( ))

return;

char str[100];

while(_________)

{

fin.getline(str,100);

cout﹤﹤str﹤﹤endl;

}

fin.close( );

}

#include ﹤iostream﹥

#include ﹤fstream﹥

using namespace std;

class complex

{

public:

int real:

int imag;

complex(int r=0, int i=0)

{

real=r;

imag=i;

}

};

complex operator+(_________,complex&b)

{

int r=a.real+b.real;

int i=a.imag+b.imag;

return _________;

}

void main( )

{

complex x(1, 2), y(3, 4), z;

z=x+y;

cout﹤﹤z.real﹤﹤"+"﹤﹤z.imag﹤﹤"i"﹤﹤endl;

}

#include ﹤iostream﹥

using namespace std;

class base

{

private: int x;

public: base(int a){x=a;}

int get( ){return x:}

void showbase( ) {cout﹤﹤"x="﹤﹤x﹤﹤endl; }

};

class Derived: public base

{private: int y;

public: Derived(int a, int b): base(a) {y=b; }

void showderived( )

{cout﹤﹤"x="﹤﹤get( )﹤﹤"，y="﹤﹤y﹤﹤endl; }

};

void main( )

{

base b(3);

Derived d(6, 7);

b.showbase( );

d.showderived( );

_________;

b.showbase( );

_________;

b1.showbase( );

base * pb=&b1;

pb-﹥showbase( );

d.showderived( );

b.showbase( );

}

输出结果如下：　　x=3　　x=6，y=7　　x=6　　x=6　　x=6　　x=6，y=7　　x=6

完成下面类中的成员函数的定义。

class point

{

private:

int m, n;

public:

point(int, int);

point(point&);

};

point:: point(int a, int b)

{

m=a;

_________=b;

}

point::point( _________ )

{

m=t.m;

n=t.n;

}

#include ﹤iostream.h﹥

class test1{

private: int x;

public: test1( ){x=2;}

void set(int a){x=a;}

void get(){cout﹤﹤x﹤﹤endl;}

};

class test2{

private: int x;

public: test2( ){x=3;}

void set(int a){x=a;}

void get( ){cout﹤﹤x﹤﹤endl;}

};

class test: public test1, public test2. {

private: int x;

public: void set(int a){x=a;}

void gettest( ){cout﹤﹤x﹤﹤endl;}

};

main( ) {

test a; a.get( );

}

#include ﹤iostream.h﹥

class f{

private: float x,y;

float get( ){return x+y;}

public：f1(float a,float b){x=a;y=b;}

};

main( ) {

f a;

a.f1(1, 3.8);

cout﹤﹤a.get( )﹤﹤endl;

}