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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).

Is there a more optimal way to concatenate this string

I was wondering if there's a more simple way to concatenate this string instead of declaring a temporary variable
string tempValue = "000000000000000" + moneyValue;
moneyValue= tempValue.Substring((tempValue).Length - 15, 15);
I'm looking to a shorter way of achieving same result , is there any?

It looks like you are looking for a more succinct way to left-pad a string with zeroes.
.NET has a built-in method for that:
moneyValue = moneyValue.PadLeft(15, '0');

PadLeft works when you start with a string. If you want to combine zero padding with formatting of a number, you can use D15 format for integers
int moneyValue = 123456;
string moneyString = $"{moneyValue:D15}";
or a custom format for other numeric types
decimal moneyValue = 1234.56;
string moneyString = $"{moneyValue:000000000000000}";

How to convert a string with a period character to an int?

How do you convert a string with a period character to an int?
I have to convert strings like "1924.912" to int's, but the int.Parse() and Convert.ToInt32() methods don't work here.

Try this:
var str = "1924.912";
var mass = str.Split('.').Select(x => x).ToArray();
Or this:
var str = "1924.912";
var mass = str.Split('.');
To have all decimal like int use next:
var str = "1924.912";
var mass = str.Replace(".","");

You can use Double.Parse() and then convert result to int.
var result = (int)Double.Parse("1924.912");
Optionally you can specify decimal separator because its local specific.
If you want get 1924912 from "1924.912" you can achieve this by replacing "." by "":
string s = "1924.912";
int result = int.Parse(s.Replace(".", ""));
result.Dump();
Will print 1924912.

Do this
string value = "34690.42724";
Convert.ToInt64(Math.Round(Convert.ToDouble(value)));

double.Parse(textBox1.Text.Replace(".",","))

If you want to convert the string "1924.912" to the integer 1924912 disregarding the period you can use this expression where you simply remove any periods in the string before doing the conversion:
Int32.Parse("1924.912".Replace(".", String.Empty))

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');

using numbers in a string

Can I use numbers while using String data type?

Sure you can, and if you want to use them as numbers you can parse the string. E.g. for an integer:
string numberAsString = "42";
int numberFromString;
if (int.TryParse(numberAsString, out numberFromString))
{
// number successfully parsed from string
}
TryParse will return a bool telling if the parsing were successful. You can also parse directly if you know the string contains a number - using Parse. This will throw if the string can't be parsed.
int number = int.Parse("42");

You can have numbers in a string.
string s = "123";
..but + will concatenate strings:
string s = "123";
string other = "4";
Debug.Assert(s + other != "127");
Debug.Assert(s + other == "1234");

Numbers can be easily represented in a string:
string str = "10";
string str = "01";
string str = 9.ToString();
However, these are strings and cannot be used as numbers directly, you can't use arithmetic operations on them and expect it to work:
"10" + "10"; // Becomes "1010"
"10" / "10"; // Will not compile

You can easily store numbers as a string:
string foo = "123";
but that only helps you if you actually want numbers in a string. For arithmetic purposes, use a number. If you need to display that later, us a format string.

String number1 = "123456";
keep in mind. using that number for arithmatic purpose, you have to convert that string into proper type like
int number1Converted = Int32.Parse(number1);
int.TryParse(number1 , out number1Converted );
for double
double doubleResult = 0.0;
double.TryParse("123.00", out doubleResult);