Initialize variables and conduct calculation in constructor : constructor « Class « C++ Tutorial

#include<iostream.h>

class box
{
   double line,width,heigth;
   double volume;
public:
   box(double a,double b,double c);
   void vol();
};

box::box(double a,double b,double c)
{
   line=a;
   width=b;
   heigth=c;
   volume=line*heigth;
}
void box::vol()
{
   cout<<"Volume is:"<<volume<<"\n";
}

main()
{
   box x(3.4,4.5,8.5),y(2.0,4.0,6.0);
   x.vol();
   y.vol();
   return 0;
}

Volume is:28.9
Volume is:12

9.2.constructor
	9.2.1.	A parameterized constructor
	9.2.2.	Use constructor to initialize class fields
	9.2.3.	Initialize variables and conduct calculation in constructor
	9.2.4.	Overload the constructor
	9.2.5.	Copy constructors
	9.2.6.	Constructor as conversion operator
	9.2.7.	Virtual copy constructor
	9.2.8.	overload constructor
	9.2.9.	Overload constructor two ways: with initializer and without initializer
	9.2.10.	Call class constructor or not during class array declaration
	9.2.11.	Call default constructor when allocating an array dynamically
	9.2.12.	Call constructor from base class to initialize fields inherited from base class
	9.2.13.	Overload constructor for different data format
	9.2.14.	Defining and using a default class constructor
	9.2.15.	Constructor parameter with default value
	9.2.16.	If a constructor only has one parameter
	9.2.17.	The default constructor for class X is one that takes no arguments;