DATA STRUCTURES - 1

Data structures and algorithms – the nightmare of most IT students. After finishing school, I, as well as my fellow students, confidently declared that: He knows us, and we don't know them. Therefore, this series of articles on "Data Structures and Algorithms" was born, the purpose is to help me review my knowledge of data structures and algorithms.

What is data structure? It is a technique for organizing and arranging data in a computer's memory. How data is sorted and organized affects how it is retrieved and used. Imagine that the memory of your computer is just your tiny attic… and the data is the items in your home, how you organize those items will affect how you find them and use them. they.

In this article, we will learn about: Arrays (Array). Shall we know what they are? Performance and how to use them?

     1. Array

A collection of data elements stored contiguously in a memory area. The elements of a must have the same data type (data type). Array elements can be accessed directly based on the index. In .Net Framework, the index starts from 0.

Consider the following example:

Statement 1: We declare an array of type integer

Statement 2: We initialize the array with 4 elements.

The allocation and initialization of memory to store the array will happen as shown below.

To work with arrays we need to know 2 types of common operations: Allocate and access.

- Allocate: this is the declaration and initialization of the array, it will allocate a memory area on the stack when we declare the array and a memory area on the heap when we initialize the size of the array.

- Access: to access any element of the array, we use index. As said .Net Framework starts from 0. With the following code, we assign the value to the 2nd element and retrieve its value to use.

The elements of the array are stored contiguously in a block of memory, and it is accessed directly through the index of the array. That's why reading and writing arrays is fast. However, the array requires a size declaration when initialized, and its elements must be of the same data type.

To decide whether to use arrays in programming or not, we need to consider three issues: do we require fast data access or do we need to be fast? Is it possible to know in advance the number of elements in a data set? And is the data type of the elements the same?

However, we can use ArrayList to replace Array in case the size of the array cannot be fixed or the datatype of the element is different.

Read More

Lập trình hướng đối tượng – OOP (2)

In my previous article, I shared some of its basic concepts: what is an object? What are classes? How is the constructor defined and used?

Next, in this article, I will present the basic features of object-oriented programming. Everyone knows when it comes to object-oriented programming, any coder, from amateur to professional, must master these characteristics. It's like the inner gong of a sect. Referring to that type of martial arts, one must immediately remember its inner gong and know how to use it. So what is the inner work of the mind of OPP? These are Abstraction, Inheritance, Encapsulation, Polymorphism.

Here we go.

First, Abstraction: It is a feature, an object-oriented principle, used to describe and display the necessary features of an object for other objects. This feature allows hiding the details of the object. It focuses on what the object does rather than how the object does it.

You can picture it like this: We have a dog, it is an object. It has action: go and eat. Dogs also have a way of walking, a dog's way of eating is different from a cat's. Abstraction, describing to the surrounding, the dog has the act of eating and walking. But how to eat, how to walk it is the dog's business, not to be described to the surroundings.

See the following code for more clarity.

Second, Encapsulation.

This means that the details of an object are restricted from being accessed by other objects, or hidden from view by other objects.

Speaking of closures, we need to know a concept called access modifier. It controls access to member data in a class. We have access modifiers: private, public, internal, protected, protected internal.

- Private: only members of the same class can access it.

- Public: unlimited access.

- Protected: only members of the class and the derived class have access.

- Internal: only members in the same assembly.

- Protected internal: members in the same assembly or inherited class are accessible.

Next, let's learn the third, Inheritance.

Defining inheritance in the object-oriented direction is the same as in social inheritance. Everyone must know who inherits, inherits from whom, and inherits what characteristics?

In object-oriented, the class to be inherited is called “superclass” or “base class”, in this class we define common features that will be inherited from subclasses. Subclasses that inherit from the parent class are called "derived classes".

The benefit of inheritance is that it can reuse code, increase system maintainability, as well as reduce the cost of system development. C# does not support multiple inheritances, to do that, we can use an interface.

An example of inheritance: We have a superclass animal: has a name property, a constructor, a move and eat method. Subclasses: dog, cat inherit from an animal class.

Implement base class

Implement derived class: Dog

Use derived class:

                

Finally Polymorphism.

Polymorphism means many forms. When a problem is handled in different ways, we call it polymorphism. We have two types of polymorphism: Compile polymorphism, or overloading, and run-time polymorphism, or overriding.

-  Overloading: a method has many different forms based on its own parameters.

- Overriding by using the keyword: virtual and override

-        

Above, you and I have gone through the 4 main slogans in object-oriented programming. Hopefully, we will memorize and use it in the best way in the Kung-fu code.

Related posts:

Part 1: OOP -1

Read More

Lập trình hướng đối tượng - OOP 1

If you are a student or a professional coder, you must have heard many times about OPP or object-oriented programming.

In my series of 2 articles, I will review the basic concepts of object-oriented programming. What is it? What are its characteristics?

OPP stands for Object oriented programming. It is a programming paradigm that is based on objects. It models real-world objects into programming objects. Those objects have the same properties and actions as in the real world. 

For example, A student is a real-world object. Student attributes height, weight, age, name... Actions: eat, sleep, walk, study. When modeled in programming, we also have an object that holds the data of student information and actions.

So each student object we create a student object in programming? It's not like that: We have concepts: object and class

What are classes?

It is a prototype of objects. It has variables that store data as well as methods of an object

We have a student class as follows

Object là gì?

Object là một thể hiện cụ thể của một đối tượng thực tế thông qua bản mẫu là một class. Khi một object được tạo thì nó sẽ được cấp phát một vùng nhớ trên heap để lưu trữ thông tin của nó.

Ví dụ: Ta có đối tượng sinh viên 1 là một thể hiện cụ thể của một sinh viên trong thực tế, qua bản mẫu là class sinh viên ta vừa tạo ở trên.

What are Objects?

The object is a concrete instance of an actual object through the template is a class. When an object is created, it will be allocated a memory area on the heap to store its information.

For example, We have student object 1 which is a specific instance of a student in reality, through the template is the student class we just created above.

Here we create a constructor with 2 variables passed in, name and age. This constructor will assign values to the member variables of the class.

When we initialize the student object with this constructor, we will pass the value of name, age.

Example: 

Using the student class creates a student object, and calls the object's self-introduction function.

Results: Just like in the real world, students use their own information to introduce others, in programming when abstracting an object, it also has the same behavior: using the information to self-identify. introduce yourself

Through this example, we can better understand: what is a class? What is an object? What is Constructor? And how to use them. In the following article, I will present the basic properties of OPP.

Related posts:

Part 2: OOP - 2

Read More