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# C++ Class member functions

A member function of a class is a function that has its definition or its prototype within the class definition like any other variable. It operates on any object of the class of which it is a member, and has access to all the members of a class for that object.

Let us take previously defined class to access the members of the class using a member function instead of directly accessing them:

    class Box
    {
       public:
          double length;         // Length of a box
          double breadth;        // Breadth of a box
          double height;         // Height of a box
          double getVolume(void);// Returns box volume
    };

Member functions can be defined within the class definition or separately using scope resolution operator, ::. Defining a member function within the class definition declares the function inline, even if you do not use the inline specifier. So either you can define Volume() function as below:

    class Box
    {
       public:
          double length;      // Length of a box
          double breadth;     // Breadth of a box
          double height;      // Height of a box

          double getVolume(void)
          {
             return length * breadth * height;
          }
    };

If you like you can define same function outside the class using scope resolution operator, :: as follows:

    double Box::getVolume(void)
    {
        return length * breadth * height;
    }

Here only important point is that you would have to use class name just before :: operator. A member function will be called using an dot operator (.) on a object where it will manipulate data related to that object only as follows:

    Box myBox;          // Create an object

    myBox.getVolume();  // Call member function for the object

Let us put above concepts to set and get the value of different class members in a class:

    #include <iostream>

    using namespace std;

    class Box
    {
       public:
          double length;         // Length of a box
          double breadth;        // Breadth of a box
          double height;         // Height of a box

          // Member functions declaration
          double getVolume(void);
          void setLength( double len );
          void setBreadth( double bre );
          void setHeight( double hei );
    };

    // Member functions definitions
    double Box::getVolume(void)
    {
        return length * breadth * height;
    }

    void Box::setLength( double len )
    {
        length = len;
    }

    void Box::setBreadth( double bre )
    {
        breadth = bre;
    }

    void Box::setHeight( double hei )
    {
        height = hei;
    }

    // Main function for the program
    int main( )
    {
       Box Box1;                // Declare Box1 of type Box
       Box Box2;                // Declare Box2 of type Box
       double volume = 0.0;     // Store the volume of a box here

       // box 1 specification
       Box1.setLength(6.0);
       Box1.setBreadth(7.0);
       Box1.setHeight(5.0);

       // box 2 specification
       Box2.setLength(12.0);
       Box2.setBreadth(13.0);
       Box2.setHeight(10.0);

       // volume of box 1
       volume = Box1.getVolume();
       cout << "Volume of Box1 : " << volume <<endl;

       // volume of box 2
       volume = Box2.getVolume();
       cout << "Volume of Box2 : " << volume <<endl;
       return 0;
    }

When the above code is compiled and executed, it produces following result:

    Volume of Box1 : 210
    Volume of Box2 : 1560

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