static class ExtensionMethods
{
    internal static bool IsBetween(this double number,double bound1, double bound2)
    {
        return Math.Min(bound1, bound2) <= number && number <= Math.Max(bound2, bound1);
    }

    internal static bool IsBetween(this int number, double bound1, double bound2)
    {
        return Math.Min(bound1, bound2) <= number && number <= Math.Max(bound2, bound1);
    }
}

使用

double numberToBeChecked = 7;

var result = numberToBeChecked.IsBetween（100，122）;

var result = 5.IsBetween（100，120）;

var result = 8.0.IsBetween（1.2，9.6）;

好吧，我会配合的。已经有这么多答案了，但也许还有一些其他新奇的空间:

(显然你根本不用这些)

    var num = 7;
    const int min = 5;
    const int max = 10;
    var inRange = Math.Clamp(num, min, max) == num;

Or

    var num = 7;
    const int min = 5;
    const int max = 10;
    var inRange = num switch { < min => false, > max => false, _ => true };

Or

    var num = 7;
    const int min = 5;
    const int max = 10;
    var inRange = num is >= min and <= max;

好吧，也许你可以用最后一个。

好的，再来一个

    var num = 7;
    const int min = 5;
    const int max = 10;
    var inRange = Enumerable.Range(min, max-min).Contains(num);

In C, if time efficiency is crucial and integer overflows will wrap, one could do if ((unsigned)(value-min) <= (max-min)) .... If 'max' and 'min' are independent variables, the extra subtraction for (max-min) will waste time, but if that expression can be precomputed at compile time, or if it can be computed once at run-time to test many numbers against the same range, the above expression may be computed efficiently even in the case where the value is within range (if a large fraction of values will be below the valid range, it may be faster to use if ((value >= min) && (value <= max)) ... because it will exit early if value is less than min).

不过，在使用这样的实现之前，请先对目标机器进行基准测试。在某些处理器上，由两部分组成的表达式可能在所有情况下都更快，因为两个比较可能是独立完成的，而在减法和比较方法中，减法必须在比较执行之前完成。

您可以使用模式匹配以最优雅的方式实现这一点:

int i = 5;
if(i is (>0 and <=10))
{

}

像这样的怎么样?

if (theNumber.isBetween(low, high, IntEx.Bounds.INCLUSIVE_INCLUSIVE))
{
}

扩展方法如下(已测试):

public static class IntEx
{
    public enum Bounds 
    {
        INCLUSIVE_INCLUSIVE, 
        INCLUSIVE_EXCLUSIVE, 
        EXCLUSIVE_INCLUSIVE, 
        EXCLUSIVE_EXCLUSIVE
    }

    public static bool isBetween(this int theNumber, int low, int high, Bounds boundDef)
    {
        bool result;
        switch (boundDef)
        {
            case Bounds.INCLUSIVE_INCLUSIVE:
                result = ((low <= theNumber) && (theNumber <= high));
                break;
            case Bounds.INCLUSIVE_EXCLUSIVE:
                result = ((low <= theNumber) && (theNumber < high));
                break;
            case Bounds.EXCLUSIVE_INCLUSIVE:
                result = ((low < theNumber) && (theNumber <= high));
                break;
            case Bounds.EXCLUSIVE_EXCLUSIVE:
                result = ((low < theNumber) && (theNumber < high));
                break;
            default:
                throw new System.ArgumentException("Invalid boundary definition argument");
        }
        return result;
    }
}

因为所有其他答案都不是我发明的，这里只是我的实现:

public enum Range
{
    /// <summary>
    /// A range that contains all values greater than start and less than end.
    /// </summary>
    Open,
    /// <summary>
    /// A range that contains all values greater than or equal to start and less than or equal to end.
    /// </summary>
    Closed,
    /// <summary>
    /// A range that contains all values greater than or equal to start and less than end.
    /// </summary>
    OpenClosed,
    /// <summary>
    /// A range that contains all values greater than start and less than or equal to end.
    /// </summary>
    ClosedOpen
}

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

    /// <summary>
    /// Checks if a value is within the given range.
    /// </summary>
    /// <param name="value">The value that should be checked.</param>
    /// <param name="start">The first value of the range to be checked.</param>
    /// <param name="end">The last value of the range to be checked.</param>
    /// <param name="range">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.</param>
    /// <returns><c>True</c> if the value is within the given range, otherwise <c>false</c>.</returns>
    public static bool IsWithin<T>(this T value, T start, T end, Range range) where T : IComparable<T>
    {
        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));
        }
    }
}

然后你可以这样使用它:

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

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