Object-oriented programming is a powerful way to approach the task of programming. Since its early beginnings, programming has been governed by various methodologies. At each hard point in the evolution of c++ programming, a new approach was created to help the programmer



handle increasingly complex programs. The first programs were created by toggling switches on the front panel of the computer. Obviously, this approach is suitable for only the smallest programs. Next, assembly language was invented, which allowed longer programs to be written. The next advance happened in the 1950s when first high-level language (FORTRAN) was invented.

By using a high-level language, a programmer was able to write programs that were several thousand lines long. However, the method of programming used early on was an ad hoc, anything-goes approach. While this is fine for relatively short programs, it yields unreadable (and unmanageable) ”spaghetti code” when applied to larger programs. The elimination of spaghetti code became feasible with the invention of structured programming languages in the 1970s. These languages include Algol and Pascal. In loose terms, C is a structured language, and most likely the type of programming you have been doing would be called structured programming. structured programming relies on well-defined control structures, code blocks, the absence (or at least minimal use) of the GOTO, and stand-alone subroutines that support recursion and local variables.Using structured programming, the average programmer can create and maintain programs that are up to 50,000 lines long.

Although structured programming has yielded excellent results when applied to moderately complex programs, even it fails at some point, after a program reaches a certain size. To allow more complex programs to be written, a new approach to the job of programming was needed. Towards this end, object oriented programming was invented. OOP takes the best of the ideas embodied in structured programming and combines them with powerful new concepts that allow you to organize your programs more effectively. Object oriented programming encourages you to decompose a problem into its constituent parts. Each component becomes a self-contained object that contains its own instructions and data that relate to that object. In this way, complexity is reduced and the programmer can manage larger programs.

All OOP languages, including C++, share three common defining traits: encapsulation, polymorphism, and inheritance. Let’s look at these concepts now.


ENCAPSULATION of object oriented programming

Encapsulation is the mechanism that binds together code and the data it manipulates and keeps both safes from outside interference and misuse. In an object oriented programming language, code and data can be combined in such a way that a self-contained ”black box” is created. When code and data are linked together in this fashion, an object is created. In other words, an object is a device that supports encapsulation.

Within an object, code, data, or both may be private to that object or public. Private code or data is known to and accessible only by another part of the object. That is, private code or data cannot be accessed by a piece of the program that exists outside the object. When code or data is public, other parts of your program can access it even though it is defined within an object. Typically, the public parts of an object are used to provide a controlled interface to the private elements of the object.

For all intents and purposes, an object is a variable of a user-defined type. It may seem strange that an object that links both code and data can be thought of as a variable. However, in object-oriented programming, this is precisely the case. Each time you define a new type of object, you are creating a new data type. Each specific instance of this data type is a compound variable.


POLYMORPHISM of object oriented programming

Polymorphism (meaning ”many forms”) is the quality that allows one name to be used for two or more related but technically different purposes. As it relates to OOP, polymorphism allows one name to specify a general class of actions. Within a general class of actions, the specific action to be applied is determined by the type of data. For example, in C, which does not significantly support polymorphism, the absolute value action requires three distinct function names: abs(), labs(), and fabs(). These functions compute and return the absolute value of an integer, a long integer, and a floating-point value, respectively. However, in C++, which supports polymorphism, each function can be called by the same name, such as abs(). (One way this can be accomplished is shown later in this chapter.) The type of data used to call the function determines which specific version of the function is actually executed. As you will see, in C++, it is possible to use one function name for many different purposes. This is called function overloading.

More generally, the concept of polymorphism is characterized by the idea of ”one interface, multiple methods,” which means using a generic interface for a group of related activities. The advantage of polymorphism is that it helps to reduce complexity by allowing one interface to specify a general class of action. It is the compiler’s job to select the specific action as it applies to each situation. You, the programmer, don’t need to do this selection manually. You need only remember and utilize the general interface. As the example in the preceding paragraph illustrates, having three names for the absolute value function instead of just one makes the general activity of obtaining the absolute value of a number more complex than it actually is.

Polymorphism can be applied to operators, too. Virtually all programming languages contain a limited application of polymorphism as it relates to the arithmetic operators. For example, in C, the + sign is used to add integers, long integers, characters, and floating-point values. In these cases, the compiler automatically knows which type of arithmetic to apply. In C++, you can extend this concept to other types of data that you define. This type of polymorphism is called operator overloading.

The key point to remember about polymorphism is that it allows you to handle greater complexity by allowing the creation of standard interfaces to related activities.


INHERITANCE of object oriented programming

Inheritance is the process by which one object can acquire the properties of another. More specifically, an object can inherit a general set of properties to which it can add those features that are specific only to itself. Inheritance is important because it allows an object to support the concept of hierarchical classification. Most information is made manageable by hierarchical classification. For example, think about the description of a house. A house is apart of the general class called building. In turn, building is part of the more general class structure, which is part of the even more general class of objects that we call man-made. In each case, the child class inherits all those qualities associated with the parent and adds to them its own defining characteristics. Without the use of ordered classifications, each object would have to define all characteristics that relate to it explicitly. However, through inheritance, it is possible to describe an object by stating what general class (or classes) it belongs to along with those specific traits that make it unique. As you will see, inheritance plays a very important role in OOP.


EXAMPLES of object oriented programming

Encapsulation is not entirely new to OOP. To a degree, encapsulation can be achieved when using the C language. For example, when you use a library function, you are, in effect, using a black-box routine, the internals of which you cannot alter or affect ( except, perhaps, through malicious actions). Consider the fopen() function. When it is used to open a file, several internal variables are created and initialized. As far as your program is concerned, these variables are hidden and not accessible. However, C++ provides a much more secure approach to encapsulation.


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