So why not?-CodePudding

Const double PI=3.14159;
The class Circle
{
Public:
Circle (double r);
Double Circumference ();
Double Area ();
Friend double fCircle_L (Circle & amp; The rr);
Friend double fCircle_S (Circle & amp; The rr);
Private:
Double radius;
};
Circle: : Circle (double r)
{
The radius=r;
}
Double Circle: : Circumference ()
{
Cout & lt; Return 2 * PI * radius;
}
Double Circle: : Area ()
{
Cout & lt; Radius, return PI * * radius;
}
Double fCircle_L (Circle & amp; R)
{
Cout & lt; Double L=2 * PI * r.r adius;
return L;
}
Double fCircle_S (Circle & amp; R)
{
Cout & lt; Double S=PI * r.r adius * r.r adius;
Return S;
}

CodePudding user response:

1. Static constants should use static modification;
2. There are structural default to 0, it should have the default parameters (double r=0);
3. Inside the perimeter of the function c1 is what? Can not, only the return that sentence is ok; (in the area of the function similarly)
4. Ask a friend function of the circumference in direct return 2 * PI * ok, a friend function can direct access to the private members; Another function in the same way ()

CodePudding user response:

Reference:

 # include 
using namespace std; 

The class Circle 
{

Public: 

Circle (double r); 
Circle (const Circle & amp; C);//copy constructor 
~ Circle (); 

Void setRadius (double r); 
Double getRadius (); 
Double Circumference (); 
Double area (); 
Friend double fCircle_L (Circle & amp; R); 
Friend double fCircle_S (Circle & amp; R); 
Private: 
The static const double PI;//=3.1415; 
double radius;//radius 
}; 

Const double Circle: : PI=3.1415; 

Circle: : Circle (double r=0) 
{
The radius=r; 
Cout<& lt;" The Constructor run "& lt; } 

Circle: : Circle (const Circle & amp; C) 
{
The radius=c.r adius; 
Cout<& lt;" CopyConstructor run "& lt; } 

Circle: : ~ Circle () 
{
Cout<& lt;" Destructor run "& lt; } 

Void Circle: : setRadius (double r) 
{
The radius=r; 
} 

Double Circle: : getRadius () 
{
Return the radius. 
} 

Double Circle: : Circumference () 
{
Return 2 * PI * radius; 
} 

Double Circle: : area () 
{
Radius, return PI * * radius; 
} 

Double fCircle_L (Circle & amp; R) 
{
Return 2 * I * r.r r.P adius; 
//return r.C ircumference (); 
} 

Double fCircle_S (Circle & amp; R) 
{
Return r.P I * r.r adius * r.r adius; 
//return of state Richard armitage rea (); 
} 

Int main (void) 
{
Double r; 
Cin & gt;> r; 

Circle c1; 
C1. SetRadius (r); 
CoutCout
Circle the c2 (c1); 
Cout & lt; Cout & lt; 
return 0; 
}