<div>
just a quick guess... you probably need to check the ascii of the input char, then you need that ascii + 1
</div>

<div>
I would try to map A, B, ..., Z to 0, 1, ..., 25, and then use base 26 to get the next (output) value.
</div>

<div>
Modulo 26 counters numbering the length of the input string with each counter carrying to the next. &nbsp;In the special case of a carry out of the high counter, the output string becomes &quot;A&quot; repeated (length of input string +1) times. &nbsp;Works no matter how long the string is. 
 

<pre><code class="code-1 nolinks" id="code-20-41859742-1">Input Counters Successor Output
AA 00 00 00 01 AB
AZ 00 25 01 00+C BA
ABB 00 01 01 00 01 02 ABC
BZZ 01 25 25 02 00+C 00+C CAA
ZZZ 25 25 25 00+C 00+C 00+C AAAA
</code></pre>
</div>

<div>
You piqued my interest. I don't know how this would be done in C# or VB.NET. But in javascript, I believe the following would work:
<pre><code class="code-10 nolinks" id="code-20-41859746-1">function incrementString(input) {
 // create an array for holding all the letters, and
 // a boolean for if the string has been incremeneted
 var inputArray = [],
 inced = false;
 // work through the string backward
 for (var i = input.length-1; i&gt;-1; i--) {
 if (inced === false) { // if a character has yet to be incremented
 if (input.charAt(i) !== 'Z') { // if the character is NOT a Z
 // insert into the beginning of the array the next
 // ASCII character after the current character
 inputArray.unshift(String.fromCharCode(input.charCodeAt(i)+1) );
 // the string has been incremented
 inced = true;
 } else {
 // if the character IS a Z, insert an A into the beginning
 // of the array and increment the next character
 inputArray.unshift('A');
 }
 } else {
 // if the string has already been incremented, just insert
 // the current character into the beginning of the array
 inputArray.unshift(input.charAt(i) );
 }
 }
 // if the string still has not been incremented, add an A to the string
 if (inced === false) {
 inputArray.unshift('A');
 }
 // join the characters in the array and return the joined string
 return inputArray.join('');
}
console.log(incrementString('ABZ') );
// should return 'ACA'
</code></pre>
</div>

<div>
Not sure if it fits author requirements but it can be done in few lines in C#: 
 

<pre><code class="code-10 nolinks" id="code-20-41861072-1"> private static string increaseChars(string input)
 {
 List&lt;char&gt; outChars= new List&lt;char&gt;();
 foreach (char ch in input.ToCharArray())
 {
 int newCharCode = ((int)ch&lt;90)? ch+1 : 65;
 outChars.Add((char) newCharCode);
 }
 return new string(outChars.ToArray());
 }
</code></pre>
 
========================================= 
 
You may test it in the following Console application: 
 

<pre><code class="code-10 nolinks" id="code-20-41861072-2"> class Program
 {
 static void Main(string[] args)
 {
 string input = &quot;ABCD&quot;;
 Console.WriteLine(input);
 Console.WriteLine(increaseChars(input));
 Console.WriteLine(&quot;==============================&quot;);
 input = &quot;AZZZ&quot;;
 Console.WriteLine(input);
 Console.WriteLine(increaseChars(input));
 Console.WriteLine(&quot;==============================&quot;);
 input = &quot;XYZXYZ&quot;;
 Console.WriteLine(input);
 Console.WriteLine(increaseChars(input));
 Console.WriteLine(&quot;==============================&quot;);
 Console.ReadLine();
 }
 private static string increaseChars(string input)
 {
 List&lt;char&gt; outChars= new List&lt;char&gt;();
 foreach (char ch in input.ToCharArray())
 {
 int newCharCode = ((int)ch&lt;90)? ch+1 : 65;
 outChars.Add((char) newCharCode);
 }
 return new string(outChars.ToArray());
 }
 }
</code></pre>
</div>

<div>
No, it fails for a string like ZZZ which should output as AAAA but becomes AAA only. 
 
/gustav
</div>

<div>
Wow, didn't notice the requirement. A bit strange one... 
 
OK, just forget. Didn't read carefully ... :)
</div>

<div>
Well, basically this is just a base 26 number system with members represented by letters from A to Z. 
 
/gustav
</div>

<div>
<blockquote>
No, it fails for a string like ZZZ which should output as AAAA but becomes AAA only.
</blockquote>
 
Reaslly, someone is wrong, either author or you. &nbsp;Or me :). If ZZZ should output as AAAA then AZ (see author's examples) should output as BAA. Or do I miss something?
</div>

<div>
Yes, a new letter, A, is only prefixed (as a carryover) when a leading Z will be raised by 1. 
 
/gustav
</div>

<div>
Can be something like: 
 

<pre><code class="code-10 nolinks" id="code-20-41861383-1"> private static string increaseChars(string input)
 {
 char[] outChars= new char[input.Length];
 char[] inputChars = input.ToCharArray();
 for (int i = 0; i &lt; input.Length; i++)
 {
 int newCharCode = (inputChars[i] &lt; 90) ? inputChars[i]+1 : 65;
 outChars[i] = (char)newCharCode;
 }
 string result = inputChars[0] == 90 ? 'A' + (new string(outChars)) : new string(outChars);
 if (result.Length&gt;4) { result = result.Substring(0, 4); }// if you want to restrict by 4 chars
 return result;
 }
</code></pre>
 
Testing: 
 

<pre><code class="code-10 nolinks" id="code-20-41861383-2"> string input = &quot;ABCD&quot;;
 Console.WriteLine(input);
 Console.WriteLine(increaseChars(input));
 Console.WriteLine(&quot;==============================&quot;);
 input = &quot;AZZZ&quot;;
 Console.WriteLine(input);
 Console.WriteLine(increaseChars(input));
 Console.WriteLine(&quot;==============================&quot;);
 input = &quot;ZZZ&quot;;
 Console.WriteLine(input);
 Console.WriteLine(increaseChars(input));
 Console.WriteLine(&quot;==============================&quot;);
 input = &quot;Z&quot;;
 Console.WriteLine(input);
 Console.WriteLine(increaseChars(input));
 Console.WriteLine(&quot;==============================&quot;);
 input = &quot;ZAB&quot;;
 Console.WriteLine(input);
 Console.WriteLine(increaseChars(input));
 Console.WriteLine(&quot;==============================&quot;);
 input = &quot;ZZZZ&quot;;
 Console.WriteLine(input);
 Console.WriteLine(increaseChars(input));
 Console.WriteLine(&quot;==============================&quot;);
 Console.ReadLine();
</code></pre>
</div>

<div>
<pre><code class="code-10 nolinks" id="code-20-41861832-1">Private Function convertBase(input As Integer, radix As Integer) As String
 Dim result = &quot;&quot;
 Dim a = Asc(&quot;A&quot;)
 Do While input &gt; -1
 Dim x = input Mod radix
 result = Chr(a + x) &amp; result
 input = Math.Floor(input / radix) - 1
 Loop
 Return result
End Function

Private Function parseBase(input As String, radix As Integer) As Integer
 Dim length = input.Length
 Dim a = Asc(&quot;A&quot;)
 Dim result As Integer
 For Each c As Char In input
 Dim x = Asc(c) - a + 1
 result += x * Math.Pow(radix, length - 1)
 length -= 1
 Next
 Return result - 1
End Function
</code></pre>
Using:
<pre><code class="code-1 nolinks" id="code-20-41861832-2">For i = 0 To 5000
 Debug.Print(i &amp; &quot;; &quot; &amp; convertBase(i, 26))
Next
</code></pre>
<pre><code class="code-1 nolinks" id="code-20-41861832-3">Dim x = parseBase(&quot;AZZZ&quot;, 26)
Debug.Print convertBase(x + 1, 26) 'BAAA
</code></pre>
</div>

<div>
PS. To validate input string in parseBase function, add
<pre><code class="code-1 nolinks" id="code-20-41861877-1"> input = input.ToUpper
If Not System.Text.RegularExpressions.Regex.IsMatch(input, &quot;[A-Z]&quot;) Then
 Throw New ArgumentException(&quot;Only letters A to Z allowed.&quot;, &quot;input&quot;)
 Return -1
End If
</code></pre>
</div>

<div>
C# 

<pre><code class="code-10 nolinks" id="code-20-41861909-1">private string convertBase(int input, int radix)
{
 string result = &quot;&quot;;
 int a = Convert.ToInt32('A');
 while (input &gt; -1)
 {
 int x = input % radix;
 result = Convert.ToChar(a + x) + result;
 input = (int)Math.Floor((double)(input / radix)) - 1;
 }
 return result;
}

private int parseBase(string input, int radix)
{
 input = input.ToUpper();
 if (!System.Text.RegularExpressions.Regex.IsMatch(input, &quot;[A-Z]&quot;))
 {
 throw new ArgumentException(&quot;Only letters A to Z allowed.&quot;, &quot;input&quot;);
 }
 int length = input.Length;
 int a = Convert.ToInt32('A');
 int result = 0;
 foreach (char c in input)
 {
 int x = Convert.ToInt32(c) - a + 1;
 result += x * (int)Math.Pow(radix, length - 1);
 length -= 1;
 }
 return result - 1;
}
</code></pre>
</div>

<div>
Wow. Thanks (all) for all the excellent comments, suggestions and samples. 
I had no idea that this would cause such a whirlwind of activity. 
Awesome.
</div>

<div>
<div class="content wysiwyg-content">
Hi: 
 
I have an interesting problem I need to solve. 
I'm sure that someone has encountered this somewhere 
and that an elegant solution exists. 
 
I'm trying to write an method which increments and returns the next 
alphanumeric character in a sequence. 
 
These letters are intended to range from 'A' to 'ZZZZ'. 
I am only dealing with capital (uppercase letters) 
 
Consider the following examples: 
 

<pre><code class="code-1 nolinks" id="code-10-28978909-1"> INPUT OUTPUT
 ===================
 A B
 G H
 Z AA
 AZ BA
 AZZZ BAAA
</code></pre>
 
I'm looking for a solution which is more or less portable across 
languages (C#, VB.Net, JavaScript/JQuery). This of course rules out 
trying something with LINQ. 
 
I've made several attempts at this, but the all are kind of klunky. 
Any thoughts, ideas, suggestions or directions to explore would be greatly appreciated. 
 
Thanks, 
JohnB
</div>
</div>

Hi:

I have an interesting problem I need to solve.
I'm sure that someone has encountered this somewhere
and that an elegant solution exists.

I'm trying to write an method which increments and returns the next
alphanumeric character in a sequence.

These letters are intended to range from 'A' to 'ZZZZ'.
I am only dealing with capital (uppercase letters)

Consider the following examples:

(CODE)

I'm looking for a solution which is more or less portable across
languages (C#, VB.Net, JavaScript/JQuery). This of course rules out
trying something with LINQ.

I've made several attempts at this, but the all are kind of klunky.
Any thoughts, ideas, suggestions or directions to explore would be greatly appreciated.

Thanks,
JohnB

What is a good method for incrementing a string sequence from &quot;A&quot; to &quot;ZZZZ&quot; in C# or vb.Net?

C# is an object-oriented programming language created in conjunction with Microsoft’s .NET framework. Compilation is usually done into the Microsoft Intermediate Language (MSIL), which is then JIT-compiled to native code (and cached) during execution in the Common Language Runtime (CLR).

Visual Basic .NET (VB.NET) is an object-oriented programming language implemented on the .NET framework, but also supported on other platforms such as Mono and Silverlight. Microsoft launched VB.NET as the successor to the Visual Basic language. Though it is similar in syntax to  Visual Basic pre-2002, it is not the same technology,

Visual Basic.NET

JavaScript is a dynamic, object-based language commonly used for client-side scripting in web browsers. Recently, server side JavaScript frameworks have also emerged. JavaScript runs on nearly every operating system and  in almost every mainstream web browser.

JavaScript

jQuery (Core) is a cross-browser JavaScript library that provides abstractions for common client-side tasks such as Document Object Model (DOM) traversal, DOM manipulation, event handling, animation and Ajax. jQuery also provides a platform to create plugins that extend jQuery's capabilities beyond those already provided by the library.

jQuery

An algorithm is a self-contained step-by-step set of operations to be performed. Algorithms exist that perform calculation, data processing, and automated reasoning. Starting from an initial state and initial input (perhaps empty), the instructions describe a computation that, when executed, proceeds through a finite number of well-defined successive states, eventually producing "output" and terminating at a final ending state. The transition from one state to the next is not necessarily deterministic; some algorithms, known as randomized algorithms, incorporate random input.

What is a good method for incrementing a string sequence from &quot;A&quot; to &quot;ZZZZ&quot; in C# or vb.Net?

What is a good method for incrementing a string sequence from "A" to "ZZZZ" in C# or vb.Net?