Is there a C# IN operator?

If you wanted to write .In then you could create an extension that allows you to do that.

static class Extensions{    public static bool In<T>(this T item, params T[] items)    {        if (items == null)            throw new ArgumentNullException("items");        return items.Contains(item);    }}class Program{    static void Main()    {        int myValue = 1;        if (myValue.In(1, 2, 3))            // Do Somthing...        string ds = "Bob";        if (ds.In("andy", "joel", "matt"))         // Do Someting...    }}

List.Contains() is I think what you're looking for. C# has in keyword and not an operator which serves completely different purpose then what you're referring in SQL.

There are two ways you can use in keyword in C#. Assume you have a string[] or List in C#.

        string[] names; //assume there are some names;        //find all names that start with "a"        var results = from str in names                      where str.StartsWith("a")                      select str;        //iterate through all names in results and print        foreach (string name in results)        {            Console.WriteLine(name);        }

Referring your edit, I'd put your code this way to do what you need.

        int myValue = 1;        List<int> checkValues = new List<int> { 1, 2, 3 };        if (checkValues.Contains(myValue))            // Do something 

You can do this:

var x = 99; // searched valueif (new[] {1,2,3,99}.Contains(x)){   // do something}