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    <p>Here's some code that uses regular expressions.</p> <p>Note that the issue raised by Bart in the comments to your question, ie. "How do you handle 1+++5", is not handled at all.</p> <p>To fix that, unless your code is already out in the wild and not subject to change of behaviour, I would suggest you change your syntax to the following:</p> <ul> <li>use .. to denote ranges</li> <li>allow both + and - for numbers, for positive and negative numbers</li> <li>use comma and/or semicolon to separate distinct numbers or ranges</li> <li>allow whitespace</li> </ul> <p>Look at the difference between the two following strings:</p> <ul> <li>1++7+10++15+20+30++</li> <li>1..7, 10..15, 20, 30..</li> </ul> <p>The second string is much easier to parse, and much easier to read.</p> <p>It would also remove all ambiguity:</p> <ul> <li>1+++5 = 1++ + 5 = 1.., 5</li> <li>1+++5 = 1 + ++5 = 1, ..5</li> </ul> <p>There's no way to parse wrong the second syntax.</p> <hr> <p>Anyway, here's my code. Basically it works by adding four regex patterns for the four types of patterns:</p> <ul> <li>num</li> <li>num++</li> <li>++num</li> <li>num++num</li> </ul> <p>For "num", it will handle negative numbers with a leading minus sign, and one or more digits. It does not, for obvious reasons, handle the plus sign as part of the number.</p> <p>I've interpreted "and up" to mean "up to Int32.MaxValue" and same for down to Int32.MinValue.</p> <pre><code>public class Range { public readonly Int32 From; public readonly Int32 To; public Range(Int32 from, Int32 to) { From = from; To = to; } public override string ToString() { if (From == To) return From.ToString(); else if (From == Int32.MinValue) return String.Format("++{0}", To); else if (To == Int32.MaxValue) return String.Format("{0}++", From); else return String.Format("{0}++{1}", From, To); } } public static class RangeSplitter { public static Range[] Split(String s) { if (s == null) throw new ArgumentNullException("s"); String[] parts = new Regex(@"(?&lt;!\+)\+(?!\+)").Split(s); List&lt;Range&gt; result = new List&lt;Range&gt;(); var patterns = new Dictionary&lt;Regex, Action&lt;Int32[]&gt;&gt;(); patterns.Add(new Regex(@"^(-?\d+)$"), values =&gt; result.Add(new Range(values[0], values[0]))); patterns.Add(new Regex(@"^(-?\d+)\+\+$"), values =&gt; result.Add(new Range(values[0], Int32.MaxValue))); patterns.Add(new Regex(@"^\+\+(-?\d+)$"), values =&gt; result.Add(new Range(Int32.MinValue, values[0]))); patterns.Add(new Regex(@"^(-?\d+)\+\+(-?\d+)$"), values =&gt; result.Add(new Range(values[0], values[1]))); foreach (String part in parts) { foreach (var kvp in patterns) { Match ma = kvp.Key.Match(part); if (ma.Success) { Int32[] values = ma.Groups .OfType&lt;Group&gt;() .Skip(1) // group 0 is the entire match .Select(g =&gt; Int32.Parse(g.Value)) .ToArray(); kvp.Value(values); } } } return result.ToArray(); } } </code></pre> <p>Unit-tests:</p> <pre><code>[TestFixture] public class RangeSplitterTests { [Test] public void Split_NullString_ThrowsArgumentNullException() { Assert.Throws&lt;ArgumentNullException&gt;(() =&gt; { var result = RangeSplitter.Split(null); }); } [Test] public void Split_EmptyString_ReturnsEmptyArray() { Range[] result = RangeSplitter.Split(String.Empty); Assert.That(result.Length, Is.EqualTo(0)); } [TestCase(01, "++7", Int32.MinValue, 7)] [TestCase(02, "7", 7, 7)] [TestCase(03, "7++", 7, Int32.MaxValue)] [TestCase(04, "1++7", 1, 7)] public void Split_SinglePatterns_ProducesExpectedRangeBounds( Int32 testIndex, String input, Int32 expectedLower, Int32 expectedUpper) { Range[] result = RangeSplitter.Split(input); Assert.That(result.Length, Is.EqualTo(1)); Assert.That(result[0].From, Is.EqualTo(expectedLower)); Assert.That(result[0].To, Is.EqualTo(expectedUpper)); } [TestCase(01, "++7")] [TestCase(02, "7++")] [TestCase(03, "1++7")] [TestCase(04, "1+7")] [TestCase(05, "1++7+10++15+20+30++")] public void Split_ExamplesFromQuestion_ProducesCorrectResults( Int32 testIndex, String input) { Range[] ranges = RangeSplitter.Split(input); String rangesAsString = String.Join("+", ranges.Select(r =&gt; r.ToString()).ToArray()); Assert.That(rangesAsString, Is.EqualTo(input)); } [TestCase(01, 10, 10, "10")] [TestCase(02, 1, 10, "1++10")] [TestCase(03, Int32.MinValue, 10, "++10")] [TestCase(04, 10, Int32.MaxValue, "10++")] public void RangeToString_Patterns_ProducesCorrectResults( Int32 testIndex, Int32 lower, Int32 upper, String expected) { Range range = new Range(lower, upper); Assert.That(range.ToString(), Is.EqualTo(expected)); } } </code></pre>
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    1. COFirst, very impressive. But - I've already suggested replacing the characters (in a way), and Svish said there could be dates and a mysterious "Anything", not just numbers.
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    2. COWoah. Will have to go through this, hehe. Some interesting things. Not sure if I quite catch what is happening with those patterns and the dictionary... but I will have a look :p (Interesting way of writing those tests too. Maybe I will rewrite mine a bit. Didn't think of using TestCase like that. What is the testIndex for? Never seen that before...)
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    3. COAnd, oh, yeah, that mysterious "Anything" isn't really that mysterious. But it can pretty much contain anything. Examples are numbers, dates, names, product ids, et cetera. No clue if they have a rule somewhere preventing people from entering a + into any of the names for example. But yeah... Not something I decided. I just have to work with it. It's kind of one of these "It's always been like that, so we can't change it"-things. I would love to make it more restrictive and better defined though...
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