Checking if HttpStatusCode represents success or failure

The accepted answer bothers me a bit as it contains magic numbers, (although they are in standard) in its second part. And first part is not generic to plain integer status codes, although it is close to my answer.

You could achieve exactly the same result by instantiating HttpResponseMessage with your status code and checking for success. It does throw an argument exception if the value is smaller than zero or greater than 999.

if (new HttpResponseMessage((HttpStatusCode)statusCode).IsSuccessStatusCode)
{
    // ...
}

This is not exactly concise, but you could make it an extension.

The HttpResponseMessage class has a IsSuccessStatusCode property, looking at the source code it is like this so as usr has already suggested 200-299 is probably the best you can do.

public bool IsSuccessStatusCode
{
    get { return ((int)statusCode >= 200) && ((int)statusCode <= 299); }
}

I am partial to the discoverability of extension methods.

public static class HttpStatusCodeExtensions
{
    public static bool IsSuccessStatusCode(this HttpStatusCode statusCode)
    {
        var asInt = (int)statusCode;
        return asInt >= 200 && asInt <= 299;
    }
}

As long as your namespace is in scope, usage would be statusCode.IsSuccessStatusCode().

If you're using the HttpClient class, then you'll get a HttpResponseMessage back.

This class has a useful property called IsSuccessStatusCode that will do the check for you.

using (var client = new HttpClient())
{
    var response = await client.PostAsync(uri, content);
    if (response.IsSuccessStatusCode)
    {
        //...
    }
}

In case you're curious, this property is implemented as:

public bool IsSuccessStatusCode
{
    get { return ((int)statusCode >= 200) && ((int)statusCode <= 299); }
}

So you can just reuse this algorithm if you're not using HttpClient directly.

You can also use EnsureSuccessStatusCode to throw an exception in case the response was not successful.