How to elegantly check if a number is within a range?

Question

How can I do this elegantly with C# and .NET 3.5/4?

For example, a number can be between 1 and 100.

I know a simple if would suffice; but the keyword to this

Answer 1

Cause all the other answer are not invented by me, here just my implementation:

public enum Range
{
    /// 

    /// A range that contains all values greater than start and less than end.
    /// 
    Open,
    /// 

    /// A range that contains all values greater than or equal to start and less than or equal to end.
    /// 
    Closed,
    /// 

    /// A range that contains all values greater than or equal to start and less than end.
    /// 
    OpenClosed,
    /// 

    /// A range that contains all values greater than start and less than or equal to end.
    /// 
    ClosedOpen
}

public static class RangeExtensions
{
    /// 

    /// Checks if a value is within a range that contains all values greater than start and less than or equal to end.
    /// 
    /// The value that should be checked.
    /// The first value of the range to be checked.
    /// The last value of the range to be checked.
    /// True if the value is greater than start and less than or equal to end, otherwise false.
    public static bool IsWithin(this T value, T start, T end) where T : IComparable
    {
        return IsWithin(value, start, end, Range.ClosedOpen);
    }

    /// 

    /// Checks if a value is within the given range.
    /// 
    /// The value that should be checked.
    /// The first value of the range to be checked.
    /// The last value of the range to be checked.
    /// The kind of range that should be checked. Depending on the given kind of range the start end end value are either inclusive or exclusive.
    /// True if the value is within the given range, otherwise false.
    public static bool IsWithin(this T value, T start, T end, Range range) where T : IComparable
    {
        if (value == null)
            throw new ArgumentNullException(nameof(value));

        if (start == null)
            throw new ArgumentNullException(nameof(start));

        if (end == null)
            throw new ArgumentNullException(nameof(end));

        switch (range)
        {
            case Range.Open:
                return value.CompareTo(start) > 0
                       && value.CompareTo(end) < 0;
            case Range.Closed:
                return value.CompareTo(start) >= 0
                       && value.CompareTo(end) <= 0;
            case Range.OpenClosed:
                return value.CompareTo(start) > 0
                       && value.CompareTo(end) <= 0;
            case Range.ClosedOpen:
                return value.CompareTo(start) >= 0
                       && value.CompareTo(end) < 0;
            default:
                throw new ArgumentException($"Unknown parameter value {range}.", nameof(range));
        }
    }
}

You can then use it like this:

var value = 5;
var start = 1;
var end = 10;

var result = value.IsWithin(start, end, Range.Closed);