Chapter 1 OO using C++

Abstract Data Types Before we begin we should know how to accomplish the goal of the program We should know all the input and output The behavior of the program is important We need to define how an item operates An item specified in terms of operations is an Abstract Data Type

Encapsulation Combining of data and related operations is called data encapsulation An object is an instance of a class An object is an instance of a class In OO languages a connection between data and member functions at the outset This allows for modeling fragments of the real world It allows for easier error finding We also can conceal details from other people

Inheritance OOLs allow for creating a hierarchy of classes The first class in the hierarchy is called the base class. Other classes are called subclasses or derived classes

Pointers Pointers are variables that contain the address of another variable We can use the pointer variable to indirectly access the value being referenced by the pointer Pointers and arrays are similar.

Pointers To create a pointer variable we use the keyword new When you want to free the memory we use the keyword delete It is an error to try to use an address that is stored in a pointer after the delete command has been issued

Pointer vs. Array for ( sum = a[0], i = 1; i < 5; i++ ) sum += a[i]; for ( sum = *a, i = 1; i < 5; i++ ) sum += *(a + i); for ( sum = *a, p = a+1; p < a+5; p++ ) sum += *p;

Why does this work? a + 1 denotes the next cell of the array. a + 1 is equivalent to &a[1] So if a = 1020, then a + 1 may not necessarily by The value will depend on the type stored in a and its sizeof value

Other pointer issues When we are dealing with dynamic data, we have issues Classes that contain dynamic data must always have a copy constructor They also must have a destructor and an assignment operator The class must take care of its data

Polymorphism Polymorphism refers to how a function name can denote many functions that are members of different objects This works because of the type of binding Static binding is determined at compile time Dynamic binding is determined at run time In order to use dynamic binding, we need two conditions to be met: Functions must be declared as virtual Functions must be declared as virtual A pointer to the object is used A pointer to the object is used