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Select text from a Richtextbox in C#

I want to select the text that is between the last '{' and '}' of a richtextbox text.
I have the next code, but I have an error on the "LastIndexOf" function and I don't know how to fix it. Can someone give me some help?
private void highlightText()
{
mRtbxOperations.SelectionStart = mRtbxOperations.Text.LastIndexOf(#"{", 1, mRtbxOperations.SelectionStart);
mRtbxOperations.SelectionLength = mRtbxOperations.Text.IndexOf(#"}", mRtbxOperations.SelectionStart, mRtbxOperations.Text.Length - 1);
mRtbxOperations.SelectionBackColor = Color.LightBlue;
mRtbxOperations.SelectionFont = new Font(mRtbxOperations.SelectionFont, FontStyle.Underline);
mRtbxOperations.SelectionLength = 0;
}
LastIndexOf Error:
The count must be positive and must refer to a location within the
string, array or collection. Parameter name: count

You LastIndexOf parameters are messed up, as well as the Length of the selection, where you need to substract the starting point in order to get the proper length.
Try a simpler version:
int textStart = mRtbxOperations.Text.LastIndexOf(#"{",
mRtbxOperations.SelectionStart);
if (textStart > -1) {
int textEnd = mRtbxOperations.Text.IndexOf(#"}", textStart);
if (textEnd > -1) {
mRtbxOperations.Select(textStart, textEnd - textStart + 1);
mRtbxOperations.SelectionBackColor = Color.LightBlue;
}
}

Seems that you're getting out of the text bounds. When you are getting a substring or an index, you always should use the string bounds, or a substring bounds. Also, you need to check that the selection is valid.
I would rewrite your code as follows:
private void highlightText()
{
Selection selection = GetSelection(mRtbxOperations.Text);
if (selection == null)
return;
mRtbxOperations.SelectionStart = selection.Start;
mRtbxOperations.SelectionLength = selection.Length;
mRtbxOperations.SelectionBackColor = Color.LightBlue;
mRtbxOperations.SelectionFont = new Font(mRtbxOperations.SelectionFont,
FontStyle.Underline);
}
private static Selection GetSelection(string text)
{
int sIndex = text.LastIndexOf(#"{");
if (sIndex == -1)
return null;
int eIndex = text.IndexOf(#"}", sIndex);
if (eIndex == -1)
return null;
return new Selection(sIndex + 1, eIndex);
}
public class Selection
{
public int Start { get; set; }
public int End { get; set; }
public int Length
{
get
{
return End - Start;
}
}
public Selection(int startIndex, int endIndex)
{
this.Start = startIndex;
this.End = endIndex;
}
}

RichTextBox is finding my search terms in funny places

I'm trying to find instances of a string in a WPF RichTextBox. What I have now almost works, but it highlights the wrong section of the document.
private int curSearchLocation;
private void FindNext_Click(object sender, RoutedEventArgs e)
{
TextRange text = new TextRange(RichEditor.Document.ContentStart, RichEditor.Document.ContentEnd);
var location = text.Text.IndexOf(SearchBox.Text, curSearchLocation, StringComparison.CurrentCultureIgnoreCase);
if (location < 0)
{
location = text.Text.IndexOf(SearchBox.Text, StringComparison.CurrentCultureIgnoreCase);
}
if (location >= 0)
{
curSearchLocation = location + 1;
RichEditor.Selection.Select(text.Start.GetPositionAtOffset(location), text.Start.GetPositionAtOffset(location + SearchBox.Text.Length));
}
else
{
curSearchLocation = 0;
MessageBox.Show("Not found");
}
RichEditor.Focus();
}
This is what happens when I search for "document":
This is because GetPositionAtOffset includes non-text elements such as opening and closing tags in its offset, which is not what I want. I couldn't find a way to ignore these elements, and I also couldn't find a way to directly get a TextPointer to the text I want, which would also solve the problem.
How can I get it to highlight the correct text?

Unfortunately the TextRange.Text strips out non-text characters, so in this case the offset computed by IndexOf will be slightly too low. That is the main problem.
I tried to solve your problem and found working solution that works fine even when we have formatted text in many paragraphs.
A lot of help is taken from this CodeProject Article. So also read that article.
int curSearchLocation;
private void FindNext_Click(object sender, RoutedEventArgs e)
{
TextRange text = new TextRange(RichEditor.Document.ContentStart, RichEditor.Document.ContentEnd);
var location = text.Text.IndexOf(SearchBox.Text, curSearchLocation, StringComparison.CurrentCultureIgnoreCase);
if (location < 0)
{
location = text.Text.IndexOf(SearchBox.Text, StringComparison.CurrentCultureIgnoreCase);
}
if (location >= 0)
{
curSearchLocation = location + 1;
Select(location, SearchBox.Text.Length);
}
else
{
curSearchLocation = 0;
MessageBox.Show("Not found");
}
RichEditor.Focus();
}
public void Select(int start, int length)
{
TextPointer tp = RichEditor.Document.ContentStart;
TextPointer tpLeft = GetPositionAtOffset(tp, start, LogicalDirection.Forward);
TextPointer tpRight = GetPositionAtOffset(tp, start + length, LogicalDirection.Forward);
RichEditor.Selection.Select(tpLeft, tpRight);
}
private TextPointer GetPositionAtOffset(TextPointer startingPoint, int offset, LogicalDirection direction)
{
TextPointer binarySearchPoint1 = null;
TextPointer binarySearchPoint2 = null;
// setup arguments appropriately
if (direction == LogicalDirection.Forward)
{
binarySearchPoint2 = this.RichEditor.Document.ContentEnd;
if (offset < 0)
{
offset = Math.Abs(offset);
}
}
if (direction == LogicalDirection.Backward)
{
binarySearchPoint2 = this.RichEditor.Document.ContentStart;
if (offset > 0)
{
offset = -offset;
}
}
// setup for binary search
bool isFound = false;
TextPointer resultTextPointer = null;
int offset2 = Math.Abs(GetOffsetInTextLength(startingPoint, binarySearchPoint2));
int halfOffset = direction == LogicalDirection.Backward ? -(offset2 / 2) : offset2 / 2;
binarySearchPoint1 = startingPoint.GetPositionAtOffset(halfOffset, direction);
int offset1 = Math.Abs(GetOffsetInTextLength(startingPoint, binarySearchPoint1));
// binary search loop
while (isFound == false)
{
if (Math.Abs(offset1) == Math.Abs(offset))
{
isFound = true;
resultTextPointer = binarySearchPoint1;
}
else
if (Math.Abs(offset2) == Math.Abs(offset))
{
isFound = true;
resultTextPointer = binarySearchPoint2;
}
else
{
if (Math.Abs(offset) < Math.Abs(offset1))
{
// this is simple case when we search in the 1st half
binarySearchPoint2 = binarySearchPoint1;
offset2 = offset1;
halfOffset = direction == LogicalDirection.Backward ? -(offset2 / 2) : offset2 / 2;
binarySearchPoint1 = startingPoint.GetPositionAtOffset(halfOffset, direction);
offset1 = Math.Abs(GetOffsetInTextLength(startingPoint, binarySearchPoint1));
}
else
{
// this is more complex case when we search in the 2nd half
int rtfOffset1 = startingPoint.GetOffsetToPosition(binarySearchPoint1);
int rtfOffset2 = startingPoint.GetOffsetToPosition(binarySearchPoint2);
int rtfOffsetMiddle = (Math.Abs(rtfOffset1) + Math.Abs(rtfOffset2)) / 2;
if (direction == LogicalDirection.Backward)
{
rtfOffsetMiddle = -rtfOffsetMiddle;
}
TextPointer binarySearchPointMiddle = startingPoint.GetPositionAtOffset(rtfOffsetMiddle, direction);
int offsetMiddle = GetOffsetInTextLength(startingPoint, binarySearchPointMiddle);
// two cases possible
if (Math.Abs(offset) < Math.Abs(offsetMiddle))
{
// 3rd quarter of search domain
binarySearchPoint2 = binarySearchPointMiddle;
offset2 = offsetMiddle;
}
else
{
// 4th quarter of the search domain
binarySearchPoint1 = binarySearchPointMiddle;
offset1 = offsetMiddle;
}
}
}
}
return resultTextPointer;
}
int GetOffsetInTextLength(TextPointer pointer1, TextPointer pointer2)
{
if (pointer1 == null || pointer2 == null)
return 0;
TextRange tr = new TextRange(pointer1, pointer2);
return tr.Text.Length;
}
Hope so this code will work for your case.

Counting number of words in C#

I'm trying to count the number of words from a rich textbox in C# the code that I have below only works if it is a single line. How do I do this without relying on regex or any other special functions.
string whole_text = richTextBox1.Text;
string trimmed_text = whole_text.Trim();
string[] split_text = trimmed_text.Split(' ');
int space_count = 0;
string new_text = "";
foreach(string av in split_text)
{
if (av == "")
{
space_count++;
}
else
{
new_text = new_text + av + ",";
}
}
new_text = new_text.TrimEnd(',');
split_text = new_text.Split(',');
MessageBox.Show(split_text.Length.ToString ());

char[] delimiters = new char[] {' ', '\r', '\n' };
whole_text.Split(delimiters,StringSplitOptions.RemoveEmptyEntries).Length;

Since you are only interested in word count, and you don't care about individual words, String.Split could be avoided. String.Split is handy, but it unnecessarily generates a (potentially) large number of String objects, which in turn creates an unnecessary burden on the garbage collector. For each word in your text, a new String object needs to be instantiated, and then soon collected since you are not using it.
For a homework assignment, this may not matter, but if your text box contents change often and you do this calculation inside an event handler, it may be wiser to simply iterate through characters manually. If you really want to use String.Split, then go for a simpler version like Yonix recommended.
Otherwise, use an algorithm similar to this:
int wordCount = 0, index = 0;
// skip whitespace until first word
while (index < text.Length && char.IsWhiteSpace(text[index]))
index++;
while (index < text.Length)
{
// check if current char is part of a word
while (index < text.Length && !char.IsWhiteSpace(text[index]))
index++;
wordCount++;
// skip whitespace until next word
while (index < text.Length && char.IsWhiteSpace(text[index]))
index++;
}
This code should work better with cases where you have multiple spaces between each word, you can test the code online.

There are some better ways to do this, but in keeping with what you've got, try the following:
string whole_text = richTextBox1.Text;
string trimmed_text = whole_text.Trim();
// new line split here
string[] lines = trimmed_text.Split(Environment.NewLine.ToCharArray());
// don't need this here now...
//string[] split_text = trimmed_text.Split(' ');
int space_count = 0;
string new_text = "";
Now make two foreach loops. One for each line and one for counting words within the lines.
foreach (string line in lines)
{
// Modify the inner foreach to do the split on ' ' here
// instead of split_text
foreach (string av in line.Split(' '))
{
if (av == "")
{
space_count++;
}
else
{
new_text = new_text + av + ",";
}
}
}
new_text = new_text.TrimEnd(',');
// use lines here instead of split_text
lines = new_text.Split(',');
MessageBox.Show(lines.Length.ToString());
}

This was a phone screening interview question that I just took (by a large company located in CA who sells all kinds of devices that starts with a letter "i"), and I think I franked... after I got offline, I wrote this. I wish I were able to do it during interview..
static void Main(string[] args)
{
Debug.Assert(CountWords("Hello world") == 2);
Debug.Assert(CountWords(" Hello world") == 2);
Debug.Assert(CountWords("Hello world ") == 2);
Debug.Assert(CountWords("Hello world") == 2);
}
public static int CountWords(string test)
{
int count = 0;
bool wasInWord = false;
bool inWord = false;
for (int i = 0; i < test.Length; i++)
{
if (inWord)
{
wasInWord = true;
}
if (Char.IsWhiteSpace(test[i]))
{
if (wasInWord)
{
count++;
wasInWord = false;
}
inWord = false;
}
else
{
inWord = true;
}
}
// Check to see if we got out with seeing a word
if (wasInWord)
{
count++;
}
return count;
}

Have a look at the Lines property mentioned in #Jay Riggs comment, along with this overload of String.Split to make the code much simpler. Then the simplest approach would be to loop over each line in the Lines property, call String.Split on it, and add the length of the array it returns to a running count.
EDIT: Also, is there any reason you're using a RichTextBox instead of a TextBox with Multiline set to True?

I use an extension method for grabbing word count in a string. Do note, however, that double spaces will mess the count up.
public static int CountWords(this string line)
{
var wordCount = 0;
for (var i = 0; i < line.Length; i++)
if (line[i] == ' ' || i == line.Length - 1)
wordCount++;
return wordCount;
}
}

Your approach is on the right path. I would do something like, passing the text property of richTextBox1 into the method. This however won't be accurate if your rich textbox is formatting HTML, so you'll need to strip out any HTML tags prior to running the word count:
public static int CountWords(string s)
{
int c = 0;
for (int i = 1; i < s.Length; i++)
{
if (char.IsWhiteSpace(s[i - 1]) == true)
{
if (char.IsLetterOrDigit(s[i]) == true ||
char.IsPunctuation(s[i]))
{
c++;
}
}
}
if (s.Length > 2)
{
c++;
}
return c;
}

We used an adapted form of Yoshi's answer, where we fixed the bug where it would not count the last word in a string if there was no white-space after it:
public static int CountWords(string test)
{
int count = 0;
bool inWord = false;
foreach (char t in test)
{
if (char.IsWhiteSpace(t))
{
inWord = false;
}
else
{
if (!inWord) count++;
inWord = true;
}
}
return count;
}

using System.Collections;
using System;
class Program{
public static void Main(string[] args){
//Enter the value of n
int n = Convert.ToInt32(Console.ReadLine());
string[] s = new string[n];
ArrayList arr = new ArrayList();
//enter the elements
for(int i=0;i<n;i++){
s[i] = Console.ReadLine();
}
string str = "";
//Filter out duplicate values and store in arr
foreach(string i in s){
if(str.Contains(i)){
}else{
arr.Add(i);
}
str += i;
}
//Count the string with arr and s variables
foreach(string i in arr){
int count = 0;
foreach(string j in s){
if(i.Equals(j)){
count++;
}
}
Console.WriteLine(i+" - "+count);
}
}
}

int wordCount = 0;
bool previousLetterWasWhiteSpace = false;
foreach (char letter in keyword)
{
if (char.IsWhiteSpace(letter))
{
previousLetterWasWhiteSpace = true;
}
else
{
if (previousLetterWasWhiteSpace)
{
previousLetterWasWhiteSpace = false;
wordCount++;
}
}
}

public static int WordCount(string str)
{
int num=0;
bool wasInaWord=true;;
if (string.IsNullOrEmpty(str))
{
return num;
}
for (int i=0;i< str.Length;i++)
{
if (i!=0)
{
if (str[i]==' ' && str[i-1]!=' ')
{
num++;
wasInaWord=false;
}
}
if (str[i]!=' ')
{
wasInaWord=true;
}
}
if (wasInaWord)
{
num++;
}
return num;
}

class Program
{
static void Main(string[] args)
{
string str;
int i, wrd, l;
StringBuilder sb = new StringBuilder();
Console.Write("\n\nCount the total number of words in a string
:\n");
Console.Write("---------------------------------------------------
---\n");
Console.Write("Input the string : ");
str = Console.ReadLine();
l = 0;
wrd = 1;
foreach (var a in str)
{
sb.Append(a);
if (str[l] == ' ' || str[l] == '\n' || str[l] == '\t')
{
wrd++;
}
l++;
}
Console.WriteLine(sb.Replace(' ', '\n'));
Console.Write("Total number of words in the string is : {0}\n",
wrd);
Console.ReadLine();
}

This should work
input.Split(' ').ToList().Count;

This can show you the number of words in a line
string line = Console.ReadLine();
string[] word = line.Split(' ');
Console.WriteLine("Words " + word.Length);

You can also do it in this way!! Add this method to your extension methods.
public static int WordsCount(this string str)
{
return Regex.Matches(str, #"((\w+(\s?)))").Count;
}
And call it like this.
string someString = "Let me show how I do it!";
int wc = someString.WordsCount();

Auto Generate alphanumeric Unique Id with C#

Total string length is 5 chars
I have a scenario, ID starts with
A0001 and ends with A9999 then
B0001 to B9999 until F0001 to f9999
after that
FA001 to FA999 then
FB001 to FB999 until ....FFFF9
Please suggest any idea on how to create this format.

public static IEnumerable<string> Numbers()
{
return Enumerable.Range(0xA0000, 0xFFFF9 - 0xA0000 + 1)
.Select(x => x.ToString("X"));
}
You could also have an id generator class:
public class IdGenerator
{
private const int Min = 0xA0000;
private const int Max = 0xFFFF9;
private int _value = Min - 1;
public string NextId()
{
if (_value < Max)
{
_value++;
}
else
{
_value = Min;
}
return _value.ToString("X");
}
}

I am a few years late. But I hope my answer will help everyone looking for a good ID Generator. None of the previous answers work as expected and do not answer this question.
My answer fits the requirements perfectly. And more!!!
Notice that setting the _fixedLength to ZERO will create dynamically sized ID's.
Setting it to anything else will create FIXED LENGTH ID's;
Notice also that calling the overload that takes a current ID will "seed" the class and consecutive calls DO NOT need to be called with another ID. Unless you had random ID's and need the next one on each.
Enjoy!
public static class IDGenerator
{
private static readonly char _minChar = 'A';
private static readonly char _maxChar = 'C';
private static readonly int _minDigit = 1;
private static readonly int _maxDigit = 5;
private static int _fixedLength = 5;//zero means variable length
private static int _currentDigit = 1;
private static string _currentBase = "A";
public static string NextID()
{
if(_currentBase[_currentBase.Length - 1] <= _maxChar)
{
if(_currentDigit <= _maxDigit)
{
var result = string.Empty;
if(_fixedLength > 0)
{
var prefixZeroCount = _fixedLength - _currentBase.Length;
if(prefixZeroCount < _currentDigit.ToString().Length)
throw new InvalidOperationException("The maximum length possible has been exeeded.");
result = result = _currentBase + _currentDigit.ToString("D" + prefixZeroCount.ToString());
}
else
{
result = _currentBase + _currentDigit.ToString();
}
_currentDigit++;
return result;
}
else
{
_currentDigit = _minDigit;
if(_currentBase[_currentBase.Length - 1] == _maxChar)
{
_currentBase = _currentBase.Remove(_currentBase.Length - 1) + _minChar;
_currentBase += _minChar.ToString();
}
else
{
var newChar = _currentBase[_currentBase.Length - 1];
newChar++;
_currentBase = _currentBase.Remove(_currentBase.Length - 1) + newChar.ToString();
}
return NextID();
}
}
else
{
_currentDigit = _minDigit;
_currentBase += _minChar.ToString();
return NextID();
}
}
public static string NextID(string currentId)
{
if(string.IsNullOrWhiteSpace(currentId))
return NextID();
var charCount = currentId.Length;
var indexFound = -1;
for(int i = 0; i < charCount; i++)
{
if(!char.IsNumber(currentId[i]))
continue;
indexFound = i;
break;
}
if(indexFound > -1)
{
_currentBase = currentId.Substring(0, indexFound);
_currentDigit = int.Parse(currentId.Substring(indexFound)) + 1;
}
return NextID();
}
}
This is a sample of the ouput using _fixedLength = 4 and _maxDigit = 5
A001
A002
A003
A004
A005
B001
B002
B003
B004
B005
C001
C002
C003
C004
C005
AA01
AA02
AA03
AA04
AA05
AB01
AB02
AB03
AB04
AB05
AC01
AC02
AC03
AC04
AC05

see this code
private void button1_Click(object sender, EventArgs e)
{
string get = label1.Text.Substring(7); //label1.text=ATHCUS-100
MessageBox.Show(get);
string ou="ATHCUS-"+(Convert.ToInt32(get)+1).ToString();
label1.Text = ou.ToString();
}

Run this query in order to get the last ID in the database
SELECT TOP 1 [ID_COLUMN] FROM [NAME_OF_TABLE] ORDER BY [ID_COLUMN] DESC
Read the result to a variable and then run the following function on the result in order to get the next ID.
public string NextID(string lastID)
{
var allLetters = new string[] {"A", "B", "C", "D", "E", "F"};
var lastLetter = lastID.Substring(0, 1);
var lastNumber = int.Parse(lastID.Substring(1));
if (Array.IndexOf(allLetters, lastLetter) < allLetters.Length - 1 &&
lastNumber == 9999)
{
//increase the letter
lastLetter = allLetters(Array.IndexOf(allLetters, lastLetter) + 1);
lastNumber = 0;
} else {
lastLetter = "!";
}
var result = lastLetter + (lastNumber + 1).ToString("0000");
//ensure we haven't exceeded the upper limit
if (result.SubString(0, 1) == "!") {
result = "Upper Bounds Exceeded!";
}
return result;
}
DISCLAIMER
This code will only generate the first set of IDs. I do not understand the process of generating the second set.

If you need to take it from the database and do this you can use something like the following.
int dbid = /* get id from db */
string id = dbid.ToString("X5");
This should give you the format you are looking for as a direct convert from the DB ID.

How to separate character and number part from string

E.g., I would like to separate:
OS234 to OS and 234
AA4230 to AA and 4230
I have used following trivial solution, but I am quite sure that there should be a more efficient and robust solution .
private void demo()
{ string cell="ABCD4321";
int a = getIndexofNumber(cell);
string Numberpart = cell.Substring(a, cell.Length - a);
row = Convert.ToInt32(rowpart);
string Stringpart = cell.Substring(0, a);
}
private int getIndexofNumber(string cell)
{
int a = -1, indexofNum = 10000;
a = cell.IndexOf("0"); if (a > -1) { if (indexofNum > a) { indexofNum = a; } }
a = cell.IndexOf("1"); if (a > -1) { if (indexofNum > a) { indexofNum = a; } }
a = cell.IndexOf("2"); if (a > -1) { if (indexofNum > a) { indexofNum = a; } }
a = cell.IndexOf("3"); if (a > -1) { if (indexofNum > a) { indexofNum = a; } }
a = cell.IndexOf("4"); if (a > -1) { if (indexofNum > a) { indexofNum = a; } }
a = cell.IndexOf("5"); if (a > -1) { if (indexofNum > a) { indexofNum = a; } }
a = cell.IndexOf("6"); if (a > -1) { if (indexofNum > a) { indexofNum = a; } }
a = cell.IndexOf("7"); if (a > -1) { if (indexofNum > a) { indexofNum = a; } }
a = cell.IndexOf("8"); if (a > -1) { if (indexofNum > a) { indexofNum = a; } }
a = cell.IndexOf("9"); if (a > -1) { if (indexofNum > a) { indexofNum = a; } }
if (indexofNum != 10000)
{ return indexofNum; }
else
{ return 0; }
}

Regular Expressions are best suited for this kind of work:
using System.Text.RegularExpressions;
Regex re = new Regex(#"([a-zA-Z]+)(\d+)");
Match result = re.Match(input);
string alphaPart = result.Groups[1].Value;
string numberPart = result.Groups[2].Value;

Use Linq to do this
string str = "OS234";
var digits = from c in str
select c
where Char.IsDigit(c);
var alphas = from c in str
select c
where !Char.IsDigit(c);

Everyone and their mother will give you a solution using regex, so here's one that is not:
// s is string of form ([A-Za-z])*([0-9])* ; char added
int index = s.IndexOfAny(new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' });
string chars = s.Substring(0, index);
int num = Int32.Parse(s.Substring(index));

I really like jason's answer. Lets improve it a bit. We dont need regex here. My solution handle input like "H1N1":
public static IEnumerable<string> SplitAlpha(string input)
{
var words = new List<string> { string.Empty };
for (var i = 0; i < input.Length; i++)
{
words[words.Count-1] += input[i];
if (i + 1 < input.Length && char.IsLetter(input[i]) != char.IsLetter(input[i + 1]))
{
words.Add(string.Empty);
}
}
return words;
}
This solution is linear O(n).
output
"H1N1" -> ["H", "1", "N", "1"]
"H" -> ["H"]
"GH1N12" -> ["GH", "1", "N", "12"]
"OS234" -> ["OS", "234"]
Same solution with a StringBuilder
public static IEnumerable<string> SplitAlpha(string input)
{
var words = new List<StringBuilder>{new StringBuilder()};
for (var i = 0; i < input.Length; i++)
{
words[words.Count - 1].Append(input[i]);
if (i + 1 < input.Length && char.IsLetter(input[i]) != char.IsLetter(input[i + 1]))
{
words.Add(new StringBuilder());
}
}
return words.Select(x => x.ToString());
}
Try it Online!

If you want resolve more occurrences of char followed by number or vice versa you can use
private string SplitCharsAndNums(string text)
{
var sb = new StringBuilder();
for (var i = 0; i < text.Length - 1; i++)
{
if ((char.IsLetter(text[i]) && char.IsDigit(text[i+1])) ||
(char.IsDigit(text[i]) && char.IsLetter(text[i+1])))
{
sb.Append(text[i]);
sb.Append(" ");
}
else
{
sb.Append(text[i]);
}
}
sb.Append(text[text.Length-1]);
return sb.ToString();
}
And then
var text = SplitCharsAndNums("asd1 asas4gr5 6ssfd");
var tokens = text.Split(' ');

Are you doing this for sorting purposes? If so, keep in mind that Regex can kill performance for large lists. I frequently use an AlphanumComparer that's a general solution to this problem (can handle any sequence of letters and numbers in any order). I believe that I adapted it from this page.
Even if you're not sorting on it, using the character-by-character approach (if you have variable lengths) or simple substring/parse (if they're fixed) will be a lot more efficient and easier to test than a Regex.

I have used bniwredyc's answer to get Improved version of my routine:
private void demo()
{
string cell = "ABCD4321";
int row, a = getIndexofNumber(cell);
string Numberpart = cell.Substring(a, cell.Length - a);
row = Convert.ToInt32(Numberpart);
string Stringpart = cell.Substring(0, a);
}
private int getIndexofNumber(string cell)
{
int indexofNum=-1;
foreach (char c in cell)
{
indexofNum++;
if (Char.IsDigit(c))
{
return indexofNum;
}
}
return indexofNum;
}

.NET 2.0 compatible, without regex
public class Result
{
private string _StringPart;
public string StringPart
{
get { return _StringPart; }
}
private int _IntPart;
public int IntPart
{
get { return _IntPart; }
}
public Result(string stringPart, int intPart)
{
_StringPart = stringPart;
_IntPart = intPart;
}
}
class Program
{
public static Result GetResult(string source)
{
string stringPart = String.Empty;
int intPart;
var buffer = new StringBuilder();
foreach (char c in source)
{
if (Char.IsDigit(c))
{
if (stringPart == String.Empty)
{
stringPart = buffer.ToString();
buffer.Remove(0, buffer.Length);
}
}
buffer.Append(c);
}
if (!int.TryParse(buffer.ToString(), out intPart))
{
return null;
}
return new Result(stringPart, intPart);
}
static void Main(string[] args)
{
Result result = GetResult("OS234");
Console.WriteLine("String part: {0} int part: {1}", result.StringPart, result.IntPart);
result = GetResult("AA4230 ");
Console.WriteLine("String part: {0} int part: {1}", result.StringPart, result.IntPart);
result = GetResult("ABCD4321");
Console.WriteLine("String part: {0} int part: {1}", result.StringPart, result.IntPart);
Console.ReadKey();
}
}

Just use the substring function and set position inside the bracket.
String id = "DON123";
System.out.println("Id nubmer is : "+id.substring(3,6));
Answer:
Id number is: 123

use Split to seprate string from sting that use tab \t and space
string s = "sometext\tsometext\tsometext";
string[] split = s.Split('\t');
now you have an array of string that you want too easy