async and await in C#

An async function is a function that allows for asynchronous programming. It enables non-blocking execution, meaning the program can continue running while waiting for tasks like network requests or file operations to complete.

1.  The async keyword turns a method into an async method, which allows you to use the await keyword in its body. 
2. When the await keyword is applied, it suspends the calling method and yields control back to its caller until the awaited task is complete.
3. await can only be used inside an async method.

private readonly HttpClient _httpClient = new HttpClient();

[HttpGet, Route("DotNetCount")]

public async Task<int> GetDotNetCount()

{

    // Suspends GetDotNetCount() to allow the caller (the web server)

    // to accept another request, rather than blocking on this one.

    var html = await _httpClient.GetStringAsync("https://dotnetfoundation.org");

    return Regex.Matches(html, @"\.NET").Count;

}

Below is the quite clear and concise explanation:

//this is pseudocode

async Method()

{

    code;

    code;

    await something;

    moreCode;

}

When Method is invoked, it executes its contents (code; lines) up to await something;. At that point, something; is fired and the method ends like a return; was there.

something; does what it needs to and then returns.

When something; returns, execution gets back to Method and proceeds from the await onward, executing moreCode;

In a even more schematic fashion, here's what happens:

1. Method is invoked
2. code; is executed
3. something; is executed, flow goes back to the point where Method was invoked
4. execution goes on with what comes after the Method invocation
5. when something; returns, flow returns inside Method
6. moreCode; is executed and Method itself ends (yes, there could be something else await-ing on it too, and so on and so forth)

Reference: https://docs.microsoft.com