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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).

Allow insertion with special characters in database using c#

I need to allow $(dollar) ,(comma) and .(full stop) into database by converting from string to decimal.Below is the way i need to insert into database.But with my current code it is inserting as given below
decimal d = Convert.ToDecimal(value);
drNew[i] = d;
i++;

You can use this to convert from a string with currency symbol to decimal:
var num = decimal.Parse("$25,529.98", NumberStyles.Currency);
You may also pass the culture if you need/want:
var cultureInfo = new System.Globalization.CultureInfo("en-US");
var num = decimal.Parse("$25,529.98", NumberStyles.Currency, cultureInfo);

Try this one,
int number = 1234567890;
Convert.ToDecimal(number).ToString("#,##0.00");
You will get the result 1,234,567,890.00.

Your approach is backwards and not advisable. Have a hidden field that stores the numeric value and a label that displays the formatted string in currency format. Then save the numeric value.

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.

show string in a desire format

I want to show my string in a special format.
For example I have a string like this s = "00012345"; and want to show it in this format 000(123-45)
I use this code for it:
label1.text = string.format("{0,###(###-##)}",s);
But just see this for result: 00012345.
What string formatting should I be using?

As mentioned you can't format an already existing string. First you need to convert the string to an int:
int num = Int32.TryParse(s);
Then you can do the formatting whilst converting it back into a string:
label1.text = num.ToString("000(000-00)");

string s = "00012345";
string s1 = s.Substring(0,3);
string s2 = s.Substring(3,3);
string s3 = s.Substring(6);
s = string.Format("{0}({1}-{2})", s1,s2,s3);

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);