Async | Await in C#

 In C#, async and await are keywords used to write asynchronous, non-blocking code in a clean and readable way. They make it easier to run tasks in the background (like calling APIs, reading files, querying a database) without freezing the main thread or UI.

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✅ 1. What is async?

async is a modifier you apply to a method.

It tells the compiler:

“This method contains asynchronous operations and may use await.”

Example:

public async Task LoadDataAsync()
{
    // asynchronous code will go here
}

Key points:

• An async method must return:

  • Task

  • Task<T>

  • or void (only for event handlers)

• An async method can contain zero or more await keywords`.

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✅ 2. What is await?

await is used inside an async method to pause execution until the awaited task finishes — without blocking the thread.

Example:

var result = await GetDataFromServerAsync();

What happens behind the scenes:

• The method pauses at await

• Control returns to the caller

• Thread is free to do other work (UI stays responsive)

• When the task finishes, method continues from that line

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✅ Example: Without async/await (Blocking)

public string GetData()
{
    Thread.Sleep(3000);  // blocks for 3 seconds
    return "Data Loaded";
}

This freezes your UI or blocks the thread.

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✅ Example: With async/await (Non-blocking)

public async Task<string> GetDataAsync()
{
    await Task.Delay(3000); // non-blocking wait
    return "Data Loaded";
}

UI remains responsive.

 Program obj = new Program();

 String result = await obj.GetData();

 Console.WriteLine(result);

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✅ Real Example: Calling an API asynchronously

using System;
using System.Net.Http;
using System.Threading.Tasks;

internal class Program
{
    static async Task Main(string[] args)
    {
        Console.WriteLine("Fetching data...");
        
        string data = await GetUserDataAsync();
        
        Console.WriteLine("Response received:");
        Console.WriteLine(data);
        
        Console.WriteLine("Program finished");
    }

    static async Task<string> GetUserDataAsync()
    {
        using HttpClient client = new HttpClient();

        // Public test API
        string url = "https://jsonplaceholder.typicode.com/users/1";

        HttpResponseMessage response = await client.GetAsync(url);
        response.EnsureSuccessStatusCode();

        return await response.Content.ReadAsStringAsync();
    }
}

• GetStringAsync runs in background

• await waits without blocking

• Easy to read and write

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✅ Why async/await is useful?

✅ No UI freezing
✅ Better performance
✅ Efficient thread usage
✅ Clean and readable code
✅ Helps handle large workloads (API calls, file I/O, DB queries)

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