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 question is elegance  It s for my toy project not for production   This questions wasn t about speed  but about code beauty  Stop talking about efficiency and such  remember you re preaching to the choir

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How about something like this   if  theNumber isBetween low  high  IntEx Bounds INCLUSIVE INCLUSIVE         with the extension method as follows  tested    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  lt   theNumber   amp  amp   theNumber  lt   high                    break              case Bounds INCLUSIVE EXCLUSIVE                  result     low  lt   theNumber   amp  amp   theNumber  lt  high                    break              case Bounds EXCLUSIVE INCLUSIVE                  result     low  lt  theNumber   amp  amp   theNumber  lt   high                    break              case Bounds EXCLUSIVE EXCLUSIVE                  result     low  lt  theNumber   amp  amp   theNumber  lt  high                    break              default                  throw new System ArgumentException  Invalid boundary definition argument                      return result

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Regarding elegance  the closest thing to the mathematical notation  a  lt   x  lt   b  slightly improves readability   public static bool IsBetween this int value  int min  int max        return min  lt   value  amp  amp  value  lt   max      For further illustration   public static bool IsOutside this int value  int min  int max        return value  lt  min    max  lt  value

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If you want to write more code than a simple if  maybe you can  Create a Extension Method called IsBetween  public static class NumberExtensionMethods       public static bool IsBetween this long value  long Min  long Max                   return  value  gt   Min  amp  amp  value  lt   Max           if  value  gt   Min  amp  amp  value  lt   Max  return true          else return false                    Checks if this number is between 1 and 100  long MyNumber   99  MessageBox Show MyNumber IsBetween 1  100  ToString         Addendum  it s worth noting that in practice you very rarely  just check for equality   or  lt      in a codebase   Other than in the most trivial situations    Purely as an example  any game programmer would use categories something like the following in every project  as a basic matter  Note that in this example it  happens to be  using a function  Mathf Approximately  which is built in to that environment  in practice you typically have to carefully develop your own concepts of what comparisons means for computer representations of real numbers  for the type of situation you are engineering    Don t even mention that if you re doing something like  perhaps a controller  a PID controller or the like  the whole issue becomes central and very difficult  it becomes the nature of the project    BY no means is the OP question here a trivial or unimportant question   private bool FloatLessThan float a  float b            if   Mathf Approximately a b    return false      if  a lt b  return true      return false         private bool FloatLessThanZero float a            if   Mathf Approximately a 0f    return false      if  a lt 0f  return true      return false         private bool FloatLessThanOrEqualToZero float a            if   Mathf Approximately a 0f    return true      if  a lt 0f  return true      return false

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You are looking for in  1  100   That s only Pascal

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Using an  amp  amp  expression to join two comparisons is simply the most elegant way to do this  If you try using fancy extension methods and such  you run into the question of whether to include the upper bound  the lower bound  or both  Once you start adding additional variables or changing the extension names to indicate what is included  your code becomes longer and harder to read  for the vast majority of programmers   Furthermore  tools like Resharper will warn you if your comparison doesn t make sense  number  gt  100  amp  amp  number  lt  1   which they won t do if you use a method   i IsBetween 100  1      The only other comment I d make is that if you re checking inputs with the intention to throw an exception  you should consider using code contracts   Contract Requires number  gt  1  amp  amp  number  lt  100    This is more elegant than if      throw new Exception       and you could even get compile-time warnings if someone tries to call your method without ensuring that the number is in bounds first

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I would do a Range object  something like this   public class Range lt T gt  where T   IComparable       public T InferiorBoundary get private set       public T SuperiorBoundary get private set        public Range T inferiorBoundary  T superiorBoundary                InferiorBoundary   inferiorBoundary          SuperiorBoundary   superiorBoundary             public bool IsWithinBoundaries T value           return InferiorBoundary CompareTo value   gt  0  amp  amp  SuperiorBoundary CompareTo value   lt  0            Then you use it this way   Range lt int gt  myRange   new Range lt int gt  1 999   bool isWithinRange   myRange IsWithinBoundaries 3     That way you can reuse it for another type

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EDIT  New Answer provided   I was just starting out using C  when I wrote the first answer to this question  and in hindsight I now realize that my  solution  was   is naive and inefficient   My original answer  I d go with the more simple version        if Enumerable Range 1 100  Contains intInQuestion        DoStuff     A Better Way  As I haven t seen any other solution that is more efficient  according to my tests at least   I ll give it another go   New and better way that also works with negative ranges      Returns true if x is in range  min  max   else false  bool inRange int x  int min 1  int max 100    gt    x - max   x - min   lt   0      This can be used with both positive and negative ranges and defaults to a range of   1  100  inclusive  and uses x as the number to check followed by an optional range defined by min and max    Adding Examples For Good Measure  Example 1      Returns true if x is in range  min  max   else false  bool inRange int x  int min 1  int max 100    gt    x - max   x - min   lt   0    Console WriteLine inRange 25    Console WriteLine inRange 1    Console WriteLine inRange 100    Console WriteLine inRange 25  30  150    Console WriteLine inRange -25  -50  0       Returns   True True True False True   Example 2  Using a list of random ints between 1 and 150     Returns true if x is in range  min  max   else false  bool inRange int x  int min 1  int max 100    gt    x - max   x - min   lt   0       Generate 100000 ints between 1 and 150 var intsToCheck   new List lt int gt     var randGen   new Random    for int i   0  i  lt  100000    i       intsToCheck Add randGen Next 150    1      var counter   0  foreach int n in intsToCheck        if inRange n     counter     Console WriteLine   0  ints found in range 1  100   counter     Returns   66660 ints found in range 1  100    Execution Time  0 016 second s

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In C  if time efficiency is crucial and integer overflows will wrap  one could do if   unsigned  value-min   lt    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  gt   min   amp  amp   value  lt   max       because it will exit early if value is less than min    Before using an implementation like that  though  benchmark one one s target machine   On some processors  the two-part expression may be faster in all cases since the two comparisons may be done independently whereas in the subtract-and-compare method the subtraction has to complete before the compare can execute

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In production code I would simply write 1  lt   x  amp  amp  x  lt   100  This is easy to understand and very readable  Starting with C 9 0 we can write x is  gt   1 and  lt   100      Note that we must write x only once                             quot is quot  introduces a pattern matching expression                             quot and quot  is part of the pattern matching unlike the logical  quot  amp  amp  quot                             With  quot  amp  amp  quot  we would have to write  x is  gt   1  amp  amp  x is  lt   100   Here is a clever method that reduces the number of comparisons from two to one by using some math  The idea is that one of the two factors becomes negative if the number lies outside of the range and zero if the number is equal to one of the bounds  If the bounds are inclusive   x - 1     100 - x   gt   0  or  x - min     max - x   gt   0   If the bounds are exclusive   x - 1     100 - x   gt  0  or  x - min     max - x   gt  0

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Do you mean   if number  gt   1  amp  amp  number  lt   100    or   bool TestRange  int numberToCheck  int bottom  int top      return  numberToCheck  gt   bottom  amp  amp  numberToCheck  lt   top

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When checking if a  Number  is in a range you have to be clear in what you mean  and what does two numbers are equal mean  In general you should wrap all floating point numbers in what is called a  epsilon ball  this is done by picking some small value and saying if two values are this close they are the same thing       private double  epsilon   10E-9           lt summary gt          Checks if the distance between two doubles is within an epsilon          In general this should be used for determining equality between doubles           lt  summary gt           lt param name  x0  gt The orgin of intrest lt  param gt           lt param name  x  gt  The point of intrest lt  param gt           lt param name  epsilon  gt The minimum distance between the points lt  param gt           lt returns gt Returns true iff x  in  x0-epsilon  x0 epsilon  lt  returns gt      public static bool IsInNeghborhood double x0  double x  double epsilon    gt  Abs x0 - x   lt  epsilon       public static bool AreEqual double v0  double v1    gt  IsInNeghborhood v0  v1   epsilon     With these two helpers in place and assuming that if any number can be cast as a double without the required accuracy  All you will need now is an enum and another method      public enum BoundType               Open          Closed          OpenClosed          ClosedOpen         The other method follows       public static bool InRange double value  double upperBound  double lowerBound  BoundType bound   BoundType Open                bool inside   value  lt  upperBound  amp  amp  value  gt  lowerBound          switch  bound                        case BoundType Open                  return inside              case BoundType Closed                  return inside    AreEqual value  upperBound     AreEqual value  lowerBound                case BoundType OpenClosed                  return inside    AreEqual value  upperBound               case BoundType ClosedOpen                  return inside    AreEqual value  lowerBound               default                  throw new System NotImplementedException  You forgot to do something                      Now this may be far more than what you wanted  but it keeps you from dealing with rounding all the time and trying to remember if a value has been rounded and to what place  If you need to you can easily extend this to work with any epsilon and to allow your epsilon to change

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I don t know but i use this method       public static Boolean isInRange this Decimal dec  Decimal min  Decimal max  bool includesMin   true  bool includesMax   true          return  includesMin    dec  gt   min     dec  gt  min    amp  amp   includesMax    dec  lt   max     dec  lt  max        And this is the way I can use it        TestMethod      public void IsIntoTheRange                 decimal dec   54           Boolean result   false           result   dec isInRange 50  60     result   True         Assert IsTrue result            result   dec isInRange 55  60     result   False         Assert IsFalse result            result   dec isInRange 54  60     result   True         Assert IsTrue result            result   dec isInRange 54  60  false     result   False         Assert IsFalse result            result   dec isInRange 32  54  false  false    result   False         Assert IsFalse result            result   dec isInRange 32  54  false    result   True         Assert IsTrue result

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These are some Extension methods that can help    public static bool IsInRange lt T gt  this T value  T min  T max  where T   System IComparable lt T gt                return value IsGreaterThenOrEqualTo min   amp  amp  value IsLessThenOrEqualTo max               public static bool IsLessThenOrEqualTo lt T gt  this T value  T other           where T   System IComparable lt T gt                var result   value CompareTo other           return result    -1    result    0              public static bool IsGreaterThenOrEqualTo lt T gt  this T value  T other           where T   System IComparable lt T gt                var result   value CompareTo other           return result    1    result    0

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Cause all the other answer are not invented by me  here just my implementation   public enum Range            lt summary gt          A range that contains all values greater than start and less than end           lt  summary gt      Open           lt summary gt          A range that contains all values greater than or equal to start and less than or equal to end           lt  summary gt      Closed           lt summary gt          A range that contains all values greater than or equal to start and less than end           lt  summary gt      OpenClosed           lt summary gt          A range that contains all values greater than start and less than or equal to end           lt  summary gt      ClosedOpen    public static class RangeExtensions            lt summary gt          Checks if a value is within a range that contains all values greater than start and less than or equal to end           lt  summary gt           lt param name  value  gt The value that should be checked  lt  param gt           lt param name  start  gt The first value of the range to be checked  lt  param gt           lt param name  end  gt The last value of the range to be checked  lt  param gt           lt returns gt  lt c gt True lt  c gt  if the value is greater than start and less than or equal to end  otherwise  lt c gt false lt  c gt   lt  returns gt      public static bool IsWithin lt T gt  this T value  T start  T end  where T   IComparable lt T gt                return IsWithin value  start  end  Range ClosedOpen                   lt summary gt          Checks if a value is within the given range           lt  summary gt           lt param name  value  gt The value that should be checked  lt  param gt           lt param name  start  gt The first value of the range to be checked  lt  param gt           lt param name  end  gt The last value of the range to be checked  lt  param gt           lt param name  range  gt 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  lt  param gt           lt returns gt  lt c gt True lt  c gt  if the value is within the given range  otherwise  lt c gt false lt  c gt   lt  returns gt      public static bool IsWithin lt T gt  this T value  T start  T end  Range range  where T   IComparable lt T gt                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   gt  0                         amp  amp  value CompareTo end   lt  0              case Range Closed                  return value CompareTo start   gt   0                         amp  amp  value CompareTo end   lt   0              case Range OpenClosed                  return value CompareTo start   gt  0                         amp  amp  value CompareTo end   lt   0              case Range ClosedOpen                  return value CompareTo start   gt   0                         amp  amp  value CompareTo end   lt  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

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static class ExtensionMethods       internal static bool IsBetween this double number double bound1  double bound2                return Math Min bound1  bound2   lt   number  amp  amp  number  lt   Math Max bound2  bound1              internal static bool IsBetween this int number  double bound1  double bound2                return Math Min bound1  bound2   lt   number  amp  amp  number  lt   Math Max bound2  bound1             Usage   double numberToBeChecked   7   var result   numberToBeChecked IsBetween 100 122    var result   5 IsBetween 100 120    var result   8 0 IsBetween 1 2 9 6

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I propose this   public static bool IsWithin lt T gt  this T value  T minimum  T maximum  where T   IComparable lt T gt        if  value CompareTo minimum   lt  0         return false      if  value CompareTo maximum   gt  0         return false      return true      Examples   45 IsWithin 32  89  true 87 2 IsWithin 87 1  87 15  false 87 2 IsWithin 87 1  87 25  true   and of course with variables   myvalue IsWithin min  max    It s easy to read  close to human language  and works with any comparable type  integer  double  custom types        Having code easy to read is important because the developer will not waste  brain cycles  to understand it  In long coding sessions wasted brain cycles make developer tired earlier and prone to bug

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Elegant because it doesn t require you to determine which of the two boundary values is greater first  It also contains no branches   public static bool InRange float val  float a  float b           Determine if val lies between a and b without first asking which is larger  a or b      return   a  lt   val  amp  val  lt  b       b  lt   val  amp  val  lt  a

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A new twist on an old favorite   public bool IsWithinRange int number  int topOfRange  int bottomOfRange  bool includeBoundaries        if  includeBoundaries          return number  lt   topOfRange  amp  amp  number  gt   bottomOfRange      return number  lt  topOfRange  amp  amp  number  gt  bottomOfRange

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If this is incidental  a simple if is all you need  If this happens in many places  you might want to consider these two    PostSharp  Decorate methods with attributes that  inject  code into the method after compilation  I don t know for sure  but I can imagine it can be used for this     Something like    Between  parameter   0  100   public void Foo int parameter         Code contracts  Has the advantage that the constraints can be checked at compile time  by static verification of your code and the places that use your code

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With a bit of extension method abuse  we can get the following  elegant  solution   using System   namespace Elegant       public class Range           public int Lower   get  set            public int Upper   get  set               public static class Ext           public static Range To this int lower  int upper                return new Range   Lower   lower  Upper   upper                       public static bool In this int n  Range r                return n  gt   r Lower  amp  amp  n  lt   r Upper                       class Program           static void Main                 int x   55              if  x In 1 To 100                    Console WriteLine  it s in range  elegantly

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I was looking for an elegant way to do it where the bounds might be switched  ie  not sure which order the values are in    This will only work on newer versions of C  where the    exists  bool ValueWithinBounds float val  float bounds1  float bounds2        return bounds1  gt   bounds2         val  lt   bounds1  amp  amp  val  gt   bounds2          val  lt   bounds2  amp  amp  val  gt   bounds1      Obviously you could change the   signs in there for your purposes  Could get fancy with type casting too  I just needed a float return within bounds  or equal to

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If it s to validate method parameters  none of the solutions throw ArgumentOutOfRangeException and allow easy proper configuration of inclusive exclusive min max values   Use like this  public void Start int pos        pos CheckRange nameof pos   min  0        if  pos IsInRange max  100  maxInclusive  false                                  I just wrote these beautiful functions  It also has the advantage of having no branching  a single if  for valid values  The hardest part is to craft the proper exception messages        lt summary gt      Returns whether specified value is in valid range       lt  summary gt       lt typeparam name  T  gt The type of data to validate  lt  typeparam gt       lt param name  value  gt The value to validate  lt  param gt       lt param name  min  gt The minimum valid value  lt  param gt       lt param name  minInclusive  gt Whether the minimum value is valid  lt  param gt       lt param name  max  gt The maximum valid value  lt  param gt       lt param name  maxInclusive  gt Whether the maximum value is valid  lt  param gt       lt returns gt Whether the value is within range  lt  returns gt  public static bool IsInRange lt T gt  this T value  T  min   null  bool minInclusive   true  T  max   null  bool maxInclusive   true      where T   struct  IComparable lt T gt        var minValid   min    null     minInclusive  amp  amp  value CompareTo min Value   gt   0       minInclusive  amp  amp  value CompareTo min Value   gt  0       var maxValid   max    null     maxInclusive  amp  amp  value CompareTo max Value   lt   0       maxInclusive  amp  amp  value CompareTo max Value   lt  0       return minValid  amp  amp  maxValid          lt summary gt      Validates whether specified value is in valid range  and throws an exception if out of range       lt  summary gt       lt typeparam name  T  gt The type of data to validate  lt  typeparam gt       lt param name  value  gt The value to validate  lt  param gt       lt param name  name  gt The name of the parameter  lt  param gt       lt param name  min  gt The minimum valid value  lt  param gt       lt param name  minInclusive  gt Whether the minimum value is valid  lt  param gt       lt param name  max  gt The maximum valid value  lt  param gt       lt param name  maxInclusive  gt Whether the maximum value is valid  lt  param gt       lt returns gt The value if valid  lt  returns gt  public static T CheckRange lt T gt  this T value  string name  T  min   null  bool minInclusive   true  T  max   null  bool maxInclusive   true  where T   struct  IComparable lt T gt        if   value IsInRange min  minInclusive  max  maxInclusive                 if  min HasValue  amp  amp  minInclusive  amp  amp  max HasValue  amp  amp  maxInclusive                        var message     0  must be between  1  and  2                 throw new ArgumentOutOfRangeException name  value  message FormatInvariant name  min  max                      else                       var messageMin   min HasValue   GetOpText true  minInclusive  FormatInvariant min    null              var messageMax   max HasValue   GetOpText false  maxInclusive  FormatInvariant max    null              var message    messageMin    null  amp  amp  messageMax    null                      0  must be  1  and  2                        0  must be  1                 throw new ArgumentOutOfRangeException name  value  message FormatInvariant name  messageMin    messageMax  messageMax                        return value     private static string GetOpText bool greaterThan  bool inclusive        return  greaterThan  amp  amp  inclusive     greater than or equal to  0             greaterThan    greater than  0             inclusive    less than or equal to  0              less than  0       public static string FormatInvariant this string format  params object    args    gt  string Format CultureInfo InvariantCulture  format  args

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As others said  use a simple if   You should think about the ordering    e g  1  lt   x  amp  amp  x  lt   100   is easier to read than  x  gt   1  amp  amp  x  lt   100

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There are a lot of options   int x   30  if  Enumerable Range 1 100  Contains x         true  if  x  gt   1  amp  amp  x  lt   100        true   Also  check out this SO post for regex options

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Just to add to the noise here  you could create an extension method   public static bool IsWithin this int value  int minimum  int maximum        return value  gt   minimum  amp  amp  value  lt   maximum      Which would let you do something like     int val   15   bool foo   val IsWithin 5 20     That being said  this seems like a silly thing to do when the check itself is only one line

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If you are concerned with the comment by  Daap on the accepted answer and can only pass the value once  you could try one of the following  bool TestRangeDistance  int numberToCheck  int bottom  int distance      return  numberToCheck  gt   bottom  amp  amp  numberToCheck  lt   bottom distance        var t   TestRangeDistance 10  somelist Count  -5  10     or   bool TestRangeMargin  int numberToCheck  int target  int margin      return  numberToCheck  gt   target-margin  amp  amp  numberToCheck  lt   target margin        var t   TestRangeMargin 10  somelist Count    5

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if  value  gt  1  amp  amp  value  lt  100           do work   else          handle outside of range logic

[c#] How to elegantly check if a number is within a range?

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