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How can i create a dynamic string format in C#

I have as input the string format CST-000000 and an integer with value 1
Upon using
string result = string.Format("CST-000000", 1);
the expected result should be CST-000001 instead of CST-000000
How could i create this string format dynamically?
For example
- CST-000 should produce CST-001
- HELLO000 should produce HELLO001
- CUSTOMER0000 should produce CUSTOMER0001

Assuming that:
You receive your format string from somewhere and you can't control what it looks like
Your format string ends with 1 or more zeros
If the format string is e.g. CST-00000 and your value is 123, you want the result to be CST-00123
You can do something like this:
Inspect your format string, and separate out the stuff at the beginning from the zeros at the end. It's easy to do this with Regex, e.g.:
string format = "CST-000000";
// "Zero or more of anything, followed by one or more zeros at the end of the string"
var match = Regex.Match(format, "(.*?)(0+)$");
if (!match.Success)
{
throw new ArgumentException("Format must end with one or more zeros");
}
string prefix = match.Groups[1].Value; // E.g. CST-
string zeros = match.Groups[2].Value; // E.g. 000000
Once you have these, note the "Zero placeholder" in this list of custom numeric format strings -- you can write e.g. 123.ToString("0000") and the output will be 0123. This lets you finish off with:
int value = 123;
string result = prefix + value.ToString(zeros);
See it on dotnetfiddle

String.Format requires a placeholder {n} with a zero-based argument number. You can also add it a format {n:format}.
string result = String.Format("CST-{0:000000}", 1);
You can also use String interpolation
string result = $"CST-{1:000000}"
The difference is that instead of a placeholder you specify the value directly (or as an expression). Instead of the Custom numeric format string, you can also use the Standard numeric format string d6: $"CST-{1:d6}"
If you want to change the format template dynamically, String.Format will work better, as you can specify the format and the value as separate arguments.
(Example assumes an enum FormatKind and C# >= 8.0)
int value = 1;
string format = formatKind switch {
FormatKind.CstSmall => "CST-{0:d3}",
FormatKind.CstLarge => "CST-{0:d6}",
FormatKind.Hello => "HELLO{0:d3}",
FormatEnum.Customer => "CUSTOMER{0:d4}"
};
string result = String.Format(format, value);
Also note that the value to be formatted must be of a numeric type. Strings cannot be formatted.
See also: Composite formatting

It seems .toString("CST-000"), .toString("HELLO000") and so on, does the trick.

ToString and String.Format can do much more than use predefined formats.
For example :
string result = string.Format("CST-{0:000000}", 1);
string result = 1.ToString("CST-000000");
Should both do what you want.
(Of course you could replace "1" by any variable, even a decimal one).

How to make string of specified length from another string c#

For example I have strings like:
"5", "8", "14", "260"
and I want to get result like:
"ST00000005", "ST00000008", "ST00000014", "ST00000260"
result string length is 10 chars. How can I do it?

I would store it as int not as string. Then you can use ToString with the appropriate format specifier D8. That has f.e. the advantage that you can increase the number:
int number = 5;
string result = String.Format("ST{0}", number.ToString("D8"));
or without ToString but only String.Format:
string result = String.Format("ST{0:D8}", number);
Read: Standard Numeric Format Strings especially Decimal ("D") Format Specifier
If you need to convert a string to int use int.Parse or int.TryParse.
For the sake of completeness, if you have to use strings use String.PadLeft(8, '0'):
string numStr = "5";
String result = String.Format("ST{0}", numStr.PadLeft(8, '0'));

int number = 5; // put the number here
string result = $"ST{number:0000000#}";
// Or:
string result = $"ST{number:D8}";
This does exactly what you want.
EDIT: Keep in mind that this is only possible in C#6

You can do this like
string s = "215";
s = s.PadLeft(8, '0').PadLeft(9,'T').PadLeft(10,'S');

Use string.Format() together with a custom format string.

Remove last characters from a string in C#. An elegant way?

I have a numeric string like this 2223,00. I would like to transform it to 2223. This is: without the information after the ",". Assume that there will be only two decimals after the ",".
I did:
str = str.Remove(str.Length - 3, 3);
Is there a more elegant solution? Maybe using another function? -I don´t like putting explicit numbers-

You can actually just use the Remove overload that takes one parameter:
str = str.Remove(str.Length - 3);
However, if you're trying to avoid hard coding the length, you can use:
str = str.Remove(str.IndexOf(','));

Perhaps this:
str = str.Split(",").First();

This will return to you a string excluding everything after the comma
str = str.Substring(0, str.IndexOf(','));
Of course, this assumes your string actually has a comma with decimals. The above code will fail if it doesn't. You'd want to do more checks:
commaPos = str.IndexOf(',');
if(commaPos != -1)
str = str.Substring(0, commaPos)
I'm assuming you're working with a string to begin with. Ideally, if you're working with a number to begin with, like a float or double, you could just cast it to an int, then do myInt.ToString() like:
myInt = (int)double.Parse(myString)
This parses the double using the current culture (here in the US, we use . for decimal points). However, this again assumes that your input string is can be parsed.

String.Format("{0:0}", 123.4567); // "123"
If your initial value is a decimal into a string, you will need to convert
String.Format("{0:0}", double.Parse("3.5", CultureInfo.InvariantCulture)) //3.5
In this example, I choose Invariant culture but you could use the one you want.
I prefer using the Formatting function because you never know if the decimal may contain 2 or 3 leading number in the future.
Edit: You can also use Truncate to remove all after the , or .
Console.WriteLine(Decimal.Truncate(Convert.ToDecimal("3,5")));

Use:
public static class StringExtensions
{
/// <summary>
/// Cut End. "12".SubstringFromEnd(1) -> "1"
/// </summary>
public static string SubstringFromEnd(this string value, int startindex)
{
if (string.IsNullOrEmpty(value)) return value;
return value.Substring(0, value.Length - startindex);
}
}
I prefer an extension method here for two reasons:
I can chain it with Substring.
Example: f1.Substring(directorypathLength).SubstringFromEnd(1)
Speed.

You could use LastIndexOf and Substring combined to get all characters to the left of the last index of the comma within the sting.
string var = var.Substring(0, var.LastIndexOf(','));

You can use TrimEnd. It's efficient as well and looks clean.
"Name,".TrimEnd(',');

Try the following. It worked for me:
str = str.Split(',').Last();

Since C# 8.0 it has been possible to do this with a range operator.
string textValue = "2223,00";
textValue = textValue[0..^3];
Console.WriteLine(textValue);
This would output the string 2223.
The 0 says that it should start from the zeroth position in the string
The .. says that it should take the range between the operands on either side
The ^ says that it should take the operand relative to the end of the sequence
The 3 says that it should end from the third position in the string

Use lastIndexOf. Like:
string var = var.lastIndexOf(',');

Formatting values

Hi i have a int example as 3 i need to format it as 003 . is the only way is convert to a string and concat and convert back ?

I guess this is what you want:
int n = 3;
string formatted = n.ToString("000");
Alternatively:
string formatted = String.Format("{0:000}", n);
More info here.

You can apply the .ToString("000"); method.

Debug.WriteLine(3.ToString("000"));
You can parse the resulting string value by using int.Parse or int.TryParse:
Debug.WriteLine(int.Parse("003"));
See Custom Numeric Format Strings

If it's an int object, the leading zeros will always be removed, regardless if you convert it to a string and back.

use the pad functionint i = 1;
i.ToString().PadLeft(3, '0');

formatting string in C#?

I've a predefined string format. For instance '>>>,>>>,>>9.99' this means that the system should display string in this '500,000,000.10'. The format can change based on the users using it. How can I write a common function to display stings on the given format passing
the input value and the format as the parameter using C#

You can use the ToString method with a standard or custom format string

For example:
string format = "{0:000,000,000.00}";
string val = 12.3456;
Console.WriteLine(string.Format(format, value)); // it prints "000,000,123.23"
You can read more about formating values here http://www.csharp-examples.net/string-format-double/

decimal value = 1.2345;
string rounded = value.ToString("d2");

private string sDecimalFormat = "0.00";
decimal d = 120M;
txtText.Text = d.ToString(sDecimalFormat);
You could then have a setting for decimal format eg:
txtText.Text = d.ToString(Settings.DecimalFormat);

String.formate can be used for formating.
Go there if you want examples
http://www.csharp-examples.net/string-format-double/

I think the following might work:
String result = String.Format(fmt.Replace('>', '#').Replace('9', '0'), inpString);
fmt being the format you want to use and inpString being the string entered by the user.
Just replace the > with # and the 9 with 0 and it'll be a valid .Net formatstring.

There is a Format method on String.
String.Format("{0:X}", 10); // prints A (hex 10)
There are several methods to format numbers, date...

I dont seem to understand how you can make 500,000,000.10 from >>>,>>>,>>9.99' but I believe the answer would be
But I assume something you are looking for is: string.Format("500,000,00{0:0.##}", 9.9915)
You can then make a method like
Public string GetString(string Format, object value)
{
return string.Format(Format, value);
}
Something like this?