Async file reading and writing in C Sharp (C#) - Mini Project: Build & Apply

Async file reading and writing

📖 Scenario: You are building a simple program that reads text from one file and writes it to another file asynchronously. This is useful when you want your program to stay responsive and not freeze while working with files.

🎯 Goal: Create a C# program that reads the content of a file called input.txt asynchronously, then writes the same content to a file called output.txt asynchronously.

📋 What You'll Learn

Use async and await keywords

Read the file input.txt asynchronously using File.ReadAllTextAsync

Write to the file output.txt asynchronously using File.WriteAllTextAsync

Print a message after writing to the file

💡 Why This Matters

🌍 Real World

Async file reading and writing is useful in apps that handle large files or many files, so the user interface stays smooth and responsive.

💼 Career

Many software jobs require working with files efficiently. Knowing async file operations helps you write better programs that don't freeze or slow down.

1

Create the initial async method and input file

Create an async method called CopyFileAsync that will handle the file operations. Inside it, declare a string variable called inputFile and set it to "input.txt". Also create a file named input.txt with the text "Hello, async world!" in your project folder.

C Sharp (C#)

using System;
using System.IO;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        // Create async method CopyFileAsync
        // Declare string inputFile = "input.txt"
        // Your code here
    }
}

Need a hint?

Remember to declare the method as async Task and create the variable inputFile with the exact value.

2

Add output file variable

Inside the CopyFileAsync method, declare a string variable called outputFile and set it to "output.txt".

C Sharp (C#)

using System;
using System.IO;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        await CopyFileAsync();
    }

    static async Task CopyFileAsync()
    {
        string inputFile = "input.txt";
        // Declare string outputFile = "output.txt"
        // Your code here
    }
}

Need a hint?

Just add the variable outputFile with the exact value inside the method.

3

Read and write files asynchronously

Inside the CopyFileAsync method, use await File.ReadAllTextAsync(inputFile) to read the content of inputFile into a string variable called content. Then use await File.WriteAllTextAsync(outputFile, content) to write the content to outputFile.

C Sharp (C#)

using System;
using System.IO;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        await CopyFileAsync();
    }

    static async Task CopyFileAsync()
    {
        string inputFile = "input.txt";
        string outputFile = "output.txt";
        // Read content asynchronously from inputFile
        // Write content asynchronously to outputFile
        // Your code here
    }
}

Need a hint?

Use await with File.ReadAllTextAsync and File.WriteAllTextAsync to read and write files asynchronously.

4

Print confirmation message

After writing the file in CopyFileAsync, add a line to print "File copied successfully!" using Console.WriteLine. This confirms the operation finished.

C Sharp (C#)

using System;
using System.IO;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        await CopyFileAsync();
    }

    static async Task CopyFileAsync()
    {
        string inputFile = "input.txt";
        string outputFile = "output.txt";
        string content = await File.ReadAllTextAsync(inputFile);
        await File.WriteAllTextAsync(outputFile, content);
        // Print confirmation message
        // Your code here
    }
}

Need a hint?

Use Console.WriteLine("File copied successfully!") to show the message after writing the file.