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How can I add a space between every 3 characters counting from the right to the left in a string in C#?

I want to add space between every 3 characters in a string in C#, but count from right to left.
For example :
11222333 -> 11 222 333

Answer by #Jimi from comments (will delete if they post their own)
var YourString = "11222333";
var sb = new StringBuilder(YourString);
for (int i = sb.Length -3; i >= 0; i -= 3)
sb.Insert(i, ' ');
return sb.ToString();
The benefit of this algorithm appears to be that you are working backwards through the string and therefore only moving a certain amount on each run, rather than the whole string.

If you are trying to format a string as a number according to some locale conventions you can use the NumberFormat class to set how you want a number to be formatted as a string
So for example
string input = "11222333";
NumberFormatInfo currentFormat = new NumberFormatInfo();
currentFormat.NumberGroupSeparator = " ";
if(Int32.TryParse(input, NumberStyles.None, currentFormat, out int result))
{
string output = result.ToString("N0", currentFormat);
Console.WriteLine(output); // 11 222 333
}

The following recursive function would do the job:
string space3(string s)
{
int len3 = s.Length - 3;
return (len <= 0) ? s
: (space3(s.Substring(0, len3)) + " " + s.Substring(len3));
}
C# 8.0 introduced string ranges. Ranges allow for a more compact form:
string space3(string s)
{
return (s.Length <= 3) ? s
: (space3(s[..^3]) + " " + s[^3..]);
}

Using Regex.Replace:
string input = "11222333";
string result = Regex.Replace( input, #"\d{3}", #" $0", RegexOptions.RightToLeft );
Demo and detailed explanation of RegEx pattern at regex101.
tl;dr: Match groups of 3 digits from right to left and replace them by space + the 3 digits.

The most efficient algorithm I can come up with is the following:
var sb = new StringBuilder(YourString.Length + YourString.Length / 3 + 1);
if (YourString.Length % 3 > 0)
{
sb.Append(YourString, 0, YourString.Length % 3);
sb.Append(' ');
}
for (var i = YourString.Length % 3; i < YourString.Length; i += 3)
{
sb.Append(YourString, i, 3);
sb.Append(' ');
}
return sb.ToString();
We first assign a StringBuilder of the correct size.
Then we check to see if we need to append the first one or two characters. Then we loop the rest.
dotnetfiddle

How to replace a particular character from string in c#?

I have a string like AX_1234X_12345_X_CXY, I want to remove X from after the first underscore _ i.e. from 1234X to 1234. So final output will be like AX_1234_12345_X_CXY. How to do it?? If I use .Replace("X", "") it will replace all X which I don't want

You can iterate trough the string from the first occurrence of '_' .
you can find the first occurrence of '_' using IndexOf().
when loop will get to 'X' it will not append it to the "fixed string".
private static void Func()
{
string Original = "AX_1234X_12345_X_CXY";
string Fixed = Original.Substring(0, Original.IndexOf("_", 0));
// in case you want to remove all 'X`s' after first occurrence of `'_'`
// just dont use that variable
bool found = false;
for (int i = Original.IndexOf("_", 0); i < Original.Length; i++)
{
if (Original[i].ToString()=="X" && found == false)
{
found = true;
}
else
{
Fixed += Original[i];
}
}
Console.WriteLine(Fixed);
Console.ReadLine();
}

Why not good old IndexOf and Substring?
string s = "AX_1234X_12345_X_CXY";
int pUnder = s.IndexOf('_');
if (pUnder >= 0) { // we have underscope...
int pX = s.IndexOf('X', pUnder + 1); // we should search for X after the underscope
if (pX >= 0) // ...as well as X after the underscope
s = s.Substring(0, pX) + s.Substring(pX + 1);
}
Console.Write(s);
Outcome:
AX_1234_12345_X_CXY

string original = #"AX_1234X_12345_X_CXY";
original = #"AX_1234_12345_X_CXY";

One way is String.Remove, because you can tell exactly where to remove from. If the offending "X" is always in the same place, you can use:
string newString = old.Remove(7,1);
This will remove 1 character starting as position 7 (counting from zero as the beginning of the string).
If not always in the same character position, you might try:
int xPos = old.IndexOf("X");
string newString = old.Remove(xPos,1);
EDIT:
Based on OP comment, the "X" we're targeting occurs just after the first underscore character, so let's index off of the first underscore:
int iPosUnderscore = old.IndexOf("_");
string newString = old.Remove(iPosUnderscore + 1 ,1); // start after the underscore

Try looking at string.IndexOf or string.IndexOfAny
string s = "AX_1234X_12345_X_CXY";
string ns = HappyChap(s);
public string HappyChap(string value)
{
int start = value.IndexOf("X_");
int next = start;
next = value.IndexOf("X_", start + 1);
if (next > 0)
{
value = value.Remove(next, 1);
}
return value;
}

If and only if this is always the format then it should be a simple matter of combining substrings of the original text without including the x in that position. But the op hasn't stated that this is always the case. So if this is always the format and the same character position is always removed then you could simply just
string s = "AX_1234X_12345_X_CXY";
string newstring = s.Substring(0, 7) + s.Substring(8);
OK, based on only the second set of numbers being variable in length, you could then do something like:
int startpos = s.IndexOf('_', 4);
string newstring = s.Substring(0, startpos - 1) + s.Substring(startpos);
with this code, the following tests resulted in:
"AX_1234X_12345_X_CXY" became "AX_1234_12345_X_CXY"
"AX_123X_12345_X_CXY" became "AX_123_12345_X_CXY"
"AX_234X_12345_X_CXY" became "AX_234_12345_X_CXY"
"AX_1X_12345_X_CXY" became "AX_1_12345_X_CXY"

Something like this could work. I'm sure there's a more elegant solution.
string input1 = "AX_1234X_12345_X_CXY";
string pattern1 = "^[A-Z]{1,2}_[0-9]{1,4}(X)";
string newInput = string.Empty;
Match match = Regex.Match(input1, pattern1);
if(match.Success){
newInput = input1.Remove(match.Groups[1].Index, 1);
}
Console.WriteLine(newInput);

count the number of points at the end of a string

I need to count the number of points at the END of string.
The number of points in the middle of the string are not relevant and should not be countet.
How can this be done?
string sample = "This.is.a.sample.string.....";
for the example above the correct answer would be 5 because there are 5 points at the end of the string.
because of performace reasons I would prefer a fast solution. Don't know if Regular Expressions
\.*$
should be used in such a case.

Start from the end of the string and go back char by char until its not a dot:
string sample = "This.is.a.sample.string....."
int count = 0;
for (int i = sample.Length - 1; i >= 0; i--)
{
if (sample[i] != '.') break;
count++;
}

Using Linq:
var test = "this.is.a.test........";
var count = test.ToCharArray().Reverse().TakeWhile(q => q == '.').Count();
Convert string to array, reverse, then take while character = '.'. Count result.

A simple solution using an extension method.
var test = "this.is.a.test........";
Console.WriteLine(test.CountTrailingDots());
public static int CountTrailingDots(this string value)
{
return value.Length - value.TrimEnd('.').Length;
}

Using Regex:
int points = Regex.Match("This.is.a.sample.string....", #"^[\w\W]*?([.]*+)$").Groups[1].Value.Length;
Description:
*+ = Matches as many characters as possible
*? = Matches as few characters as possible.

It can be something like..
string sample = "This.is.a.sample.string.....";
int count = 0;
if(sample.EndsWith("."))
count = sample.Substring(sample.TrimEnd('.').Length).Length;

C#: Increment only the last number of a String

I have strings that look like this:
1.23.4.34
12.4.67
127.3.2.21.3
1.1.1.9
This is supposed to be a collection of numbers, separated by '.' symbols, similar to an ip address. I need to increment only the last digit/digits.
Expected Output:
1.23.4.35
12.4.68
127.3.2.21.4
1.1.1.10
Basically, increment whatever the number that is after the last '.' symbol.
I tried this:
char last = numberString[numberString.Length - 1];
int number = Convert.ToInt32(last);
number = number + 1;
If I go with the above code, I just need to replace the characters after the last '.' symbol with the new number. How do I get this done, good folks? :)

It seems to me that one method would be to:
split the string on . to get an array of components.
turn the final component into an integer.
increment that integer.
turn it back into a string.
recombine the components with . characters.
See, for example, the following program:
using System;
namespace ConsoleApplication1 {
class Program {
static void Main(string[] args) {
String original = "1.23.4.34";
String[] components = original.Split('.');
int value = Int32.Parse(components[components.Length - 1]) + 1;
components[components.Length - 1] = value.ToString();
String newstring = String.Join(".",components);
Console.WriteLine(newstring);
}
}
}
which outputs the "next highest" value of:
1.23.4.35

You can use string.LastIndexOf().
string input = "127.3.2.21.4";
int lastIndex = input.LastIndexOf('.');
string lastNumber = input.Substring(lastIndex + 1);
string increment = (int.Parse(lastNumber) + 1).ToString();
string result = string.Concat(input.Substring(0, lastIndex + 1), increment);

You need to extract more than just the last character. What if the last character is a 9 and then you add 1 to it? Then you need to correctly add one to the preceding character as well. For example, the string 5.29 should be processed to become 5.30 and not simply 5.210 or 5.20.
So I suggest you split the string into its number sections. Parse the last section into an integer. Increment it and then create the string again. I leave it as an exercise for the poster to actually write the few lines of code. Good practice!

Something like this:
var ip = "1.23.4.34";
var last = int.Parse(ip.Split(".".ToCharArray(),
StringSplitOptions.RemoveEmptyEntries).Last());
last = last + 1;
ip = string.Format("{0}.{1}",ip.Remove(ip.LastIndexOf(".")) , last);
If you are dealing with IP, there will be some extra code in case of .034, which should be 035 instead of 35. But that logic is not that complicated.

It's simple as this, use Split() and Join() String methods
String test = "1.23.4.34"; // test string
String[] splits = test.Split('.'); // split by .
splits[splits.Length - 1] = (int.Parse(splits[splits.Length - 1])+1).ToString(); // Increment last integer (Note : Assume all are integers)
String answ = String.Join(".",splits); // Use string join to make the string from string array. uses . separator
Console.WriteLine(answ); // Answer : 1.23.4.35

Using a bit of Linq
int[] int_arr = numberString.Split('.').Select(num => Convert.ToInt32(num)).ToArray();
int_arr[int_arr.Length - 1]++;
numberString = "";
for(int i = 0; i < int_arr.Length; i++) {
if( i == int_arr.Length - 1) {
numberString += int_arr[i].ToString();
}
else {
numberString += (int_arr[i].ToString() + ".");
}
}
Note: on phone so can't test.

My Solution is:
private static string calcNextCode(string value, int index)
{
if (value is null) return "1";
if (value.Length == index + 1) return value + "1";
int lastNum;
int myIndex = value.Length - ++index;
char myValue = value[myIndex];
if (int.TryParse(myValue.ToString(), NumberStyles.Integer, null, out lastNum))
{
var aStringBuilder = new StringBuilder(value);
if (lastNum == 9)
{
lastNum = 0;
aStringBuilder.Remove(myIndex, 1);
aStringBuilder.Insert(myIndex, lastNum);
return calcNextCode(aStringBuilder.ToString(), index++);
}
else
{
lastNum++;
}
aStringBuilder.Remove(myIndex, 1);
aStringBuilder.Insert(myIndex, lastNum);
return aStringBuilder.ToString();
}
return calcNextCode(value, index++);
}

c# getting a string within another string

i have a string like this:
some_string = "A simple demo of SMS text messaging.\r\n+CMGW: 3216\r\n\r\nOK\r\n\"
im coming from vb.net and i need to know in c#, if i know the position of CMGW, how do i get "3216" out of there?
i know that my start should be the position of CMGW + 6, but how do i make it stop as soon as it finds "\r" ??
again, my end result should be 3216
thank you!

Find the index of \r from the start of where you're interested in, and use the Substring overload which takes a length:
// Production code: add validation here.
// (Check for each index being -1, meaning "not found")
int cmgwIndex = text.IndexOf("CMGW: ");
// Just a helper variable; makes the code below slightly prettier
int startIndex = cmgwIndex + 6;
int crIndex = text.IndexOf("\r", startIndex);
string middlePart = text.Substring(startIndex, crIndex - startIndex);

If you know the position of 3216 then you can just do the following
string inner = some_string.SubString(positionOfCmgw+6,4);
This code will take the substring of some_string starting at the given position and only taking 4 characters.
If you want to be more general you could do the following
int start = positionOfCmgw+6;
int endIndex = some_string.IndexOf('\r', start);
int length = endIndex - start;
string inner = some_string.SubString(start, length);

One option would be to start from your known index and read characters until you hit a non-numeric value. Not the most robust solution, but it will work if you know your input's always going to look like this (i.e., no decimal points or other non-numeric characters within the numeric part of the string).
Something like this:
public static int GetNumberAtIndex(this string text, int index)
{
if (index < 0 || index >= text.Length)
throw new ArgumentOutOfRangeException("index");
var sb = new StringBuilder();
for (int i = index; i < text.Length; ++i)
{
char c = text[i];
if (!char.IsDigit(c))
break;
sb.Append(c);
}
if (sb.Length > 0)
return int.Parse(sb.ToString());
else
throw new ArgumentException("Unable to read number at the specified index.");
}
Usage in your case would look like:
string some_string = #"A simple demo of SMS text messaging.\r\n+CMGW: 3216\r\n...";
int index = some_string.IndexOf("CMGW") + 6;
int value = some_string.GetNumberAtIndex(index);
Console.WriteLine(value);
Output:
3216

If you're looking to extract the number portion of 'CMGW: 3216' then a more reliable method would be to use regular expressions. That way you can look for the entire pattern, and not just the header.
var some_string = "A simple demo of SMS text messaging.\r\n+CMGW: 3216\r\n\r\nOK\r\n";
var match = Regex.Match(some_string, #"CMGW\: (?<number>[0-9]+)", RegexOptions.Multiline);
var number = match.Groups["number"].Value;

More general, if you don't know the start position of CMGW but the structure remains as before.
String s;
char[] separators = {'\r'};
var parts = s.Split(separators);
parts.Where(part => part.Contains("CMGW")).Single().Reverse().TakeWhile(c => c != ' ').Reverse();