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Who knows Enumerable.Range(...)?

By , 14 Apr 2013
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I quite often see constructs like:

for(int n = 0; n < len; ++n)
   //... some more or less complex conditional control flow...
   n = 5; // causes the loop to never terminate if len is greater than 5
   //... some more code ...

This is a legal language construct, but it introduces the danger of non-determinism.

This tip aims to show some deterministic alternatives to that plain for loop.

Using the Code

If you need to loop over some range of integer, consider using the Enumerable.Range[^] based foreach loop instead:

using System.Linq;
foreach (int n in Enumerable.Range(0, len))

This guarantees that it iterates over all elements in strict sequence. Another benefit is that you cannot assign any other value to the loop variable n. E.g.

foreach (int n in Enumerable.Range(0, len))
    n = 5; // Compiler error!

Note: Enumerable.Range(...) is not from, to, but from, count:

// Summary:
//     Generates a sequence of integral numbers within a specified range.
// Parameters:
//   start:
//     The value of the first integer in the sequence.
//   count:
//     The number of sequential integers to generate.
// Returns:
//     An IEnumerable<Int32> in C# or IEnumerable(Of Int32) in Visual Basic that
//     contains a range of sequential integral numbers.
// Exceptions:
//   System.ArgumentOutOfRangeException:
//     count is less than 0.-or-start + count -1 is larger than System.Int32.MaxValue.
public static IEnumerable<int> Range(int start, int count);


One could also build his own iterator functions (see also C# Iterator Pattern demystified[^]). E.g.

public static IEnumerable<int> CountUp(int n, int count)
    while (count-- > 0) yield return n++;
public static IEnumerable<int> CountDown(int n, int count)
    while (count-- > 0) yield return n--;

When used like this...

foreach (int n in CountUp(0, 5)) Console.WriteLine(n);
foreach (int n in CountDown(100, 5)) Console.WriteLine(n);

...results in:


You can define any complexity of traversing sequence in that function and let the foreach-loop terminate deterministically, based on that sequence.


Try to avoid plain for (...) loops and replace by some deterministic loop alternative like:

  • foreach( ... Range(...))
  • foreach( ... CountUp(...))
  • etc.

Other alternatives are Linq iterations like Enumerable.Aggregate[^] etc. But these are a bit more advanced.


  • 2012-04-18 First version
  • 2012-04-19 Added hand-crafted CountUp/CountDown functions
  • 2013-04-14 Fixed some broken HTML markup in C# code generics


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Andreas Gieriet
Founder eXternSoft GmbH
Switzerland Switzerland
I feel comfortable on a variety of systems (UNIX, Windows, cross-compiled embedded systems, etc.) in a variety of languages, environments, and tools.
I have a particular affinity to computer language analysis, testing, as well as quality management.
More information about what I do for a living can be found at my LinkedIn Profile and on my company's web page (German only).
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Comments and Discussions

GeneralMy vote of 5 PinmemberAdam Mendoza22-Apr-13 23:06 
GeneralRe: My vote of 5 PinmemberAndreas Gieriet23-Apr-13 12:59 
Generalovercoming "from, count" PinprofessionalMatt T Heffron15-Apr-13 7:38 
GeneralRe: overcoming "from, count" PinmemberAndreas Gieriet15-Apr-13 10:33 
GeneralRe: overcoming "from, count" PinprofessionalMatt T Heffron15-Apr-13 10:43 
GeneralRe: overcoming "from, count" PinmemberAndreas Gieriet15-Apr-13 12:02 
GeneralRe: overcoming "from, count" PinprofessionalMatt T Heffron15-Apr-13 12:09 
QuestionAnother readability optimization Pinmemberpaul.vencill15-Apr-13 1:09 
AnswerRe: Another readability optimization PinmemberAndreas Gieriet15-Apr-13 5:50 
GeneralThoughts PinmemberPIEBALDconsult14-Apr-13 15:30 

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