Introduction to Classes

• Classes are how c++ implements an ADT.
• What is an ADT?
  • An important idea is encapsulation.
    • The data and functions are bundled.
    • Clients or users of the class do not have direct access to the data.
• Basic Syntax

  • class Identifier {
       Access_Modifier:
           members
       Accdess_Modifier:
           members
    };
           

  • Access modifiers can be
    • public: members listed with this access modifier can be accessed by anything.
    • private: members listed with this access modifier can only be accessed by any instance of the class.
    • protected a special case we will consider in 330.
      • Do not use this for now.
  • Members are function prototypes or variable definitions.
• Access modifiers are one of the tools used to accomplish encapsulation and information hiding.
  • By placing a member in the private section you do not allow other entities to access it directly.
  • Thus they do not rely on the implementation.
  • But you need to place adequate access mechanisms in the public area.
• Classes usually have a special function called a constructor
  • This is responsible for creating an instance of the classs.
  • It is strange in that it does not have a return type.
  • But it is responsible for creating an instance of the class or "instantiating" the class.
  • It is named after the class.
  • There can be multiple of these.
  • Unless you have a good reason to do so, there should be one that takes no parameters.
  • This is called a default constructor.
• There are several other types of member functions
• observers or getters which return values stored in the class.
• transformers or setters which change values stored in the class.
• iterators which we will discuss in 330.
• destructors which we will discuss later.
• Let's write a really simple person class
  • Set the domain to be name and age.
  • What functions might we want to perform on this person?
  • Write it.
• Let's think about a fraction.
  • What is the domain of a fraction?
  • What operations can you perform on a fraction?
  • Write it.