C# Programming Tutorial: From Fundamentals to Advanced Application Development

📘 Chapter 6: File Handling, Databases, and Application Building in C#

🧠 Introduction

This chapter combines three core aspects of real-world C# development:

• File Handling – Read/write data to local storage.
• Database Connectivity – Interact with relational databases (SQL Server).
• Application Building – Create a complete working C# console application.

These skills allow developers to build practical, data-driven applications that persist and retrieve data, such as finance tools, inventory systems, or CRUD-based software.

📁 Part 1: File Handling in C#

🔹 Namespaces Required

using System;

using System.IO;

✅ Creating and Writing to a File

string filePath = "data.txt";

File.WriteAllText(filePath, "Hello, File Handling!");

Console.WriteLine("File created and data written.");

• WriteAllText() creates or overwrites the file.
• Automatically closes the file when done.

✅ Reading from a File

string content = File.ReadAllText("data.txt");

Console.WriteLine("Content: " + content);

✅ Appending Data

File.AppendAllText("data.txt", "\nNew line added.");

✅ Checking File Existence

if (File.Exists("data.txt"))

    Console.WriteLine("File found.");

else

    Console.WriteLine("File not found.");

✅ Deleting a File

File.Delete("data.txt");

📋 File Handling Methods Comparison

✅ Using StreamReader and StreamWriter

using (StreamWriter writer = new StreamWriter("sample.txt"))

{

    writer.WriteLine("Line 1");

    writer.WriteLine("Line 2");

}

csharp

CopyEdit

using (StreamReader reader = new StreamReader("sample.txt"))

{

    string line;

    while ((line = reader.ReadLine()) != null)

        Console.WriteLine(line);

}

💾 Part 2: Database Connectivity with ADO.NET

🔹 ADO.NET Overview

ADO.NET is the standard .NET API for accessing relational databases such as SQL Server, MySQL, or SQLite.

🔹 Required Namespace

using System.Data.SqlClient;

✅ Basic SQL Server Connection

string connectionString = "Server=localhost;Database=TestDB;Trusted_Connection=True;";

using SqlConnection conn = new SqlConnection(connectionString);

conn.Open();

Console.WriteLine("Connected to database!");

✅ Creating a Table

string sql = "CREATE TABLE Employees (Id INT, Name NVARCHAR(50))";

SqlCommand cmd = new SqlCommand(sql, conn);

cmd.ExecuteNonQuery();

✅ Inserting Data

string insertSql = "INSERT INTO Employees VALUES (1, 'Alice')";

SqlCommand insertCmd = new SqlCommand(insertSql, conn);

insertCmd.ExecuteNonQuery();

✅ Reading Data

string readSql = "SELECT * FROM Employees";

SqlCommand readCmd = new SqlCommand(readSql, conn);

SqlDataReader reader = readCmd.ExecuteReader();

while (reader.Read())

{

    Console.WriteLine($"ID: {reader[0]}, Name: {reader[1]}");

}

📋 ADO.NET Command Summary

🏗️ Part 3: Building a C# Console Application

Let’s combine everything into a mini project — a basic Employee Management System.

✅ Step 1: Define the Employee Class

class Employee

{

    public int Id { get; set; }

    public string Name { get; set; }

}

✅ Step 2: Create a Database Helper

class Database

{

    string connString = "Server=localhost;Database=TestDB;Trusted_Connection=True;";

    public void AddEmployee(Employee emp)

    {

        using SqlConnection conn = new SqlConnection(connString);

        conn.Open();

        string sql = $"INSERT INTO Employees VALUES ({emp.Id}, '{emp.Name}')";

        SqlCommand cmd = new SqlCommand(sql, conn);

        cmd.ExecuteNonQuery();

    }

    public void ListEmployees()

    {

        using SqlConnection conn = new SqlConnection(connString);

        conn.Open();

        SqlCommand cmd = new SqlCommand("SELECT * FROM Employees", conn);

        SqlDataReader reader = cmd.ExecuteReader();

        while (reader.Read())

        {

            Console.WriteLine($"ID: {reader["Id"]}, Name: {reader["Name"]}");

        }

    }

}

✅ Step 3: Program Logic

class Program

{

    static void Main()

    {

        Database db = new Database();

        Console.Write("Enter ID: ");

        int id = Convert.ToInt32(Console.ReadLine());

        Console.Write("Enter Name: ");

        string name = Console.ReadLine();

        db.AddEmployee(new Employee { Id = id, Name = name });

        Console.WriteLine("Employee added successfully.\n");

        Console.WriteLine("Current Employees:");

        db.ListEmployees();

    }

}

✅ Output Example

Enter ID: 1

Enter Name: Alice

Employee added successfully.

Current Employees:

ID: 1, Name: Alice

📚 Real-World Use Cases

📋 Summary Table