Makindo Medical Notes

Overview of C# Programming

C# (pronounced "C-sharp") is a modern, object-oriented programming language developed by Microsoft. It is part of the .NET framework and is used for developing a wide range of applications, from desktop and web applications to mobile and cloud-based applications. C# combines the power of C++ with the simplicity of Visual Basic, making it a versatile and easy-to-learn language.

Basic Syntax and Structure

• Comments:
  • Single-line comments start with double slashes (//).

  // This is a single-line comment

  • Multi-line comments are enclosed in /* and */.

  /* 
  This is a multi-line comment 
  spanning multiple lines 
  */

  • XML documentation comments start with triple slashes (///).

  /// 
  
  /// This is a documentation comment.
  /// 

• Main Method:
  • The entry point of a C# program is the Main method.

  using System;
  namespace HelloWorld
  {
   class Program
   {
   static void Main(string[] args)
   {
   Console.WriteLine("Hello, World!");
   }
   }
  }

• Data Types:
  • Common data types include int, float, double, char, string, and bool.

  int age = 25;
  float height = 5.9f;
  double pi = 3.14159;
  char initial = 'A';
  string name = "Alice";
  bool isActive = true;

Control Structures

• Conditional Statements:
  • if, else if, and else are used for decision making.

  if (age > 18)
  {
   Console.WriteLine("Adult");
  }
  else
  {
   Console.WriteLine("Minor");
  }

• Switch Statement:
  • Used for multi-way branching.

  switch (initial)
  {
   case 'A':
   Console.WriteLine("Grade A");
   break;
   case 'B':
   Console.WriteLine("Grade B");
   break;
   default:
   Console.WriteLine("Other Grade");
   break;
  }

• Loops:
  • for, while, and do-while loops for iteration.

  for (int i = 0; i < 5; i++)
  {
   Console.WriteLine(i);
  }
  int j = 0;
  while (j < 5)
  {
   Console.WriteLine(j);
   j++;
  }
  int k = 0;
  do
  {
   Console.WriteLine(k);
   k++;
  } while (k < 5);

Functions (Methods)

• Defining Methods:
  • Methods are defined using the return type, method name, and parameters.

  static int Add(int a, int b)
  {
   return a + b;
  }
  static void Main(string[] args)
  {
   int sum = Add(5, 3);
   Console.WriteLine("Sum: " + sum);
  }

• Void Methods:
  • Methods that do not return a value.

  static void Greet(string name)
  {
   Console.WriteLine("Hello, " + name + "!");
  }
  static void Main(string[] args)
  {
   Greet("Alice");
  }

Object-Oriented Programming

• Classes and Objects:
  • Classes define the blueprint for objects.
  • Objects are instances of classes.

  class Dog
  {
   public string Name;
   public int Age;
   public Dog(string name, int age)
   {
   Name = name;
   Age = age;
   }
   public void Bark()
   {
   Console.WriteLine(Name + " says woof!");
   }
  }
  class Program
  {
   static void Main(string[] args)
   {
   Dog myDog = new Dog("Buddy", 3);
   myDog.Bark();
   }
  }

• Inheritance:
  • Allows a class to inherit attributes and methods from another class.

  class Animal
  {
   public string Name;
   public virtual void Speak()
   {
   Console.WriteLine("Animal speaks");
   }
  }
  class Dog : Animal
  {
   public override void Speak()
   {
   Console.WriteLine(Name + " says woof!");
   }
  }
  class Program
  {
   static void Main(string[] args)
   {
   Dog myDog = new Dog();
   myDog.Name = "Buddy";
   myDog.Speak();
   }
  }

• Polymorphism:
  • Allows methods to do different things based on the object it is acting upon.

  class Animal
  {
   public virtual void Speak()
   {
   Console.WriteLine("Animal speaks");
   }
  }
  class Dog : Animal
  {
   public override void Speak()
   {
   Console.WriteLine("Dog barks");
   }
  }
  class Cat : Animal
  {
   public override void Speak()
   {
   Console.WriteLine("Cat meows");
   }
  }
  class Program
  {
   static void Main(string[] args)
   {
   Animal myDog = new Dog();
   Animal myCat = new Cat();
   myDog.Speak(); // Output: Dog barks
   myCat.Speak(); // Output: Cat meows
   }
  }

Error Handling

• Try-Catch Blocks:
  • Used to handle exceptions and prevent program crashes.

  try
  {
   int result = 10 / 0;
  }
  catch (DivideByZeroException e)
  {
   Console.WriteLine("Cannot divide by zero!");
  }

• Finally Block:
  • Code in the finally block always executes, regardless of whether an exception occurred.

  try
  {
   int result = 10 / 0;
  }
  catch (DivideByZeroException e)
  {
   Console.WriteLine("Cannot divide by zero!");
  }
  finally
  {
   Console.WriteLine("This will always be printed");
  }

Data Access

• Connecting to Databases:
  • C# can interact with databases using ADO.NET.

  using System;
  using System.Data.SqlClient;
  class Program
  {
   static void Main(string[] args)
   {
   string connectionString = "Data Source=(local);Initial Catalog=MyDatabase;Integrated Security=True";
   string query = "SELECT * FROM MyTable";
   using (SqlConnection connection = new SqlConnection(connectionString))
   {
   connection.Open();
   SqlCommand command = new SqlCommand(query, connection);
   SqlDataReader reader = command.ExecuteReader();
   while (reader.Read())
   {
   Console.WriteLine(reader["ColumnName"].ToString());
   }
   }
   }
  }

Asynchronous Programming

• Async and Await:
  • Asynchronous methods are defined using the async keyword and can use the await keyword to call other asynchronous methods.

  using System;
  using System.Net.Http;
  using System.Threading.Tasks;
  class Program
  {
   static async Task Main(string[] args)
   {
   string url = "https://jsonplaceholder.typicode.com/todos/1";
   string result = await FetchDataAsync(url);
   Console.WriteLine(result);
   }
   static async Task FetchDataAsync(string url)
   {
   using (HttpClient client = new HttpClient())
   {
   HttpResponseMessage response = await client.GetAsync(url);
   response.EnsureSuccessStatusCode();
   return await response.Content.ReadAsStringAsync();
   }
   }
  }

Graphical User Interface (GUI) Development

• Windows Forms:
  • Windows Forms is a GUI class library included as a part of the .NET Framework, providing a platform to create rich desktop applications.

  using System;
  using System.Windows.Forms;
  public class MainForm : Form
  {
   private Button button;
   public MainForm()
   {
   button = new Button();
   button.Text = "Click me";
   button.Click += new EventHandler(Button_Click);
   Controls.Add(button);
   }
   private void Button_Click(object sender, EventArgs e)
   {
   MessageBox.Show("Button clicked!");
   }
   [STAThread]
   public static void Main()
   {
   Application.Run(new MainForm());
   }
  }

• WPF (Windows Presentation Foundation):
  • WPF is a UI framework that creates desktop client applications. It uses XAML for front-end design and C# for backend logic.

  using System;
  using System.Windows;
  namespace WpfApp
  {
   public partial class MainWindow : Window
   {
   public MainWindow()
   {
   InitializeComponent();
   }
   private void Button_Click(object sender, RoutedEventArgs e)
   {
   MessageBox.Show("Button clicked!");
   }
   }
  }

Summary

C# is a powerful and versatile programming language used for developing a wide range of applications. Understanding its basic syntax, control structures, object-oriented principles, error handling, data access techniques, asynchronous programming, and GUI development is essential for building robust and efficient software. C#'s integration with the .NET framework makes it a popular choice for developers working on Windows-based applications.