{"id":221,"date":"2020-08-31T16:13:42","date_gmt":"2020-08-31T16:13:42","guid":{"rendered":"https:\/\/www.kindsonthegenius.com\/cplusplus\/?p=221"},"modified":"2020-08-31T16:13:42","modified_gmt":"2020-08-31T16:13:42","slug":"c-oop-basics","status":"publish","type":"post","link":"https:\/\/www.kindsonthegenius.com\/cplusplus\/c-oop-basics\/","title":{"rendered":"C++ OOP – Basics"},"content":{"rendered":"

We are not stepping into\u00a0 the world of OOP. Somehow, every modern programming language supports some form of OOP features.<\/p>\n

Let’s first get through the basics of OOP under the following sub-topics:<\/p>\n

    \n
  1. What is OOP?<\/a><\/li>\n
  2. Creating Classes in C++<\/a><\/li>\n
  3. Creating Objects from Class<\/a><\/li>\n
  4. Accessing Data Members and Member Functions<\/a><\/li>\n
  5. Benefits of Object Oriented Programming<\/a><\/li>\n<\/ol>\n

     <\/p>\n

    1. What is OOP?<\/strong><\/h4>\n

    OOP in C++, or in programming generally, stands for Object Oriented Programming. This is an approach to programming where programs are written based on classes<\/strong> <\/em>and objects<\/strong><\/em>. These are the two key aspect of OOP.<\/p>\n

    An object is a representation a real object. Just look around you, or just think for a minute! Everything is basically an object: phone, keyboard, mouse, pen, computer, food, camera, banana, apple, bike, car, dog etc.<\/p>\n

    So we can say an object is made up of attributes<\/em> <\/strong>and methods<\/strong><\/em>.<\/p>\n

    A class is a blueprint of an object. Basically, we can create objects from classes. In other words, an object is an instance of a class.<\/p>\n

    The figure below illustrates this:<\/p>\n

    \"Object<\/a><\/p>\n

    You can also think of fruits: apple, orange, banana, etc<\/p>\n

    How does all of this relate to programing? Well, Let’s see<\/p>\n

     <\/p>\n

    2. Creating Classes\u00a0 C++<\/strong><\/h4>\n

    Since we now know what classes an object are, we should be able to create them. We define a class in C++ using the class keyword. Then we provide the class name followed by curly braces. Inside, the curly braces, we then specify it’s attributes and methods.<\/p>\n

    Here’s a class that represents a circle<\/p>\n

    class<\/span> Square<\/span> {\r\npublic:<\/span> \r\n\tdouble<\/span> length;\r\n\tdouble<\/span> width;\r\n\t\r\n\tdouble<\/span> calculateArea<\/span>(){\r\n\t\treturn<\/span> length *<\/span> width;\r\n\t}\r\n\t\r\n\tdouble<\/span> calculatePerimeter<\/span>(){\r\n\t\treturn<\/span> 2<\/span> *<\/span> length *<\/span> width;\r\n\t}\r\n};\r\n<\/pre>\n
    So we created a class named Circle.<\/p>\n
    The variables length and width are the attributes of the class. They are also called data members<\/em><\/strong> or member variables<\/strong><\/em>.<\/p>\n
    The functions calculateArea() and calculatePerimeter() are known as member functions<\/strong><\/em>.<\/p>\n
     <\/p>\n
    3. Creating Objects from Class<\/strong><\/h4>\n
    As mentioned before, a class is a blueprint for creating objects. Therefore, once you have a class, you can start creating objects from it.<\/p>\n
    Creating objects from a class in called instantiation. So we can, “instantiate a circle<\/strong>“. In order words, create an instance of a Square or object of type, Square.<\/p>\n
    Objects are instantiated same way we create Structs<\/a> or declare variables. For example:<\/p>\n
    Square square1; \/\/Declare square1 of type Square<\/span>\r\nSquare square2; \/\/Declare square1 of type Square<\/span>\r\n<\/pre>\n
    This code instantiates two Squares, square1 and square2.<\/p>\n
     <\/p>\n
    .4. Accessing Data Members & Member Functions<\/strong><\/h4>\n
    So if we have created an object, we should be able to access it’s attributes(data members). Or we may want to call it’s member functions.<\/p>\n
    To achieve this, we use the dot(.) operator.<\/p>\n
    #include <iostream><\/span>\r\n#include \"Square.cpp\" <\/span>\/\/the class is in another file<\/span>\r\n\r\nusing<\/span> namespace<\/span> std;\r\n\r\n\/\/ main function<\/span>\r\nint<\/span> main<\/span> () {\r\n\r\n\t\/\/Create a new Square, square1<\/span>\r\n\tSquare square1;\r\n\r\n\t\/\/assign values to the data members<\/span>\r\n\tsquare1.length =<\/span> 20.2<\/span>;\r\n\tsquare1.width =<\/span> 10.5<\/span>;\r\n\r\n\t\/\/Calculate the area and perimeter<\/span>\r\n\tcout <<<\/span>\"Area is: \"<\/span> <<<\/span> square1.calculateArea()<<<\/span>endl;\r\n\tcout <<<\/span>\"Perimeter is: \"<\/span> <<<\/span> square1.calculatePerimeter() <<<\/span>endl;\r\n\r\n   return<\/span> 0<\/span>;\r\n}\r\n<\/pre>\n
    Output is:<\/p>\n
    Area is: 212.1\r\nPerimeter is: 424.2\r\n<\/pre>\n
    one thing I would you to see from the program is that the class is defined in another file, Square.cpp<\/em>. Then it is included in the main file using the #include<\/strong> directive.<\/p>\n
    Also note that the data members and member functions are declared a public. This means that they can be accessed from anywhere from the program.<\/p>\n
    Now\u00a0 we have cover some basics of OOP. But there’s yet much to learn. So let me end this lesson by mentioning few benefits of OOP<\/p>\n
     <\/p>\n
    5. Benefits of OOP<\/strong><\/h4>\n
      \n
    • make the program clearer and more readable<\/li>\n
    • OOP programs are faster in execution<\/li>\n
    • they help to create easier to maintain codes since classes can be reused<\/li>\n
    • less code and shorter development time<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"
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