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How to convert string to decimal with 3 decimal places?

string num = 23.6;
I want to know how can I convert it into decimal with 3 decimal places
like
decimal nn = 23.600
Is there any method?

I try my best..
First of all your string num = 23.6; won't even compile. You need to use double quotes with your strings like string num = "23.6";
If you wanna get this as a decimal, you need to parse it first with a IFormatProvider that have . as a NumberDecimalSeparator like InvariantCulture(if your CurrentCulture uses . already, you don't have to pass second paramter);
decimal nn = decimal.Parse(num, CultureInfo.InvariantCulture);
Now we have a 23.6 as a decimal value. But as a value, 23.6, 23.60, 23.600 and 23.60000000000 are totally same, right? No matter which one you parse it to decimal, you will get the same value as a 23.6M in debugger. Looks like these are not true. See Jon Skeet comments on this answer and his "Keeping zeroes" section on Decimal floating point in .NET article.
Now what? Yes, we need to get it's textual representation as 23.600. Since we need only decimal separator in a textual representation, The "F" Format Specifier will fits out needs.
string str = nn.ToString("F3", CultureInfo.InvariantCulture); // 23.600

There are two different concepts here.
Value
View
you can have a value of 1 and view it like 1.0 or 1.0000 or +000001.00.
you have string 23.6. you can convert it to decimal using var d = decimal.Parse("23.6")
now you have a value equals to 23.6 you can view it like 23.600 by using d.ToString("F3")
you can read more about formatting decimal values

the thing that works for me in my case is num.ToString("#######.###")

A decimal is not a string, it does not display the trailing zeros. If you want a string that displays your 3 decimal places including trailing zeros, you can use string.Format:
decimal nn= 23.5;
var formattedNumber = string.Format("{0,000}", nn);

c# Decimal issues

Code first.
taxRateDecimal = 0.0765;
if (taxRateDecimal.ToString().Split('.').Length == 2)
{
outPut = taxRateDecimal.ToString().Split('.')[1].Substring(0, 4);
ReportParameters.Add("TaxRateAsDecimal", "." + outPut);
}
As you can see in the substring I have to hard code my length of 4.
Desired results .0765 as a string.
Here are some scenarios I have gone through.
I have a percent of 7.65.
I want to convert this to decimal, when doing so I do 7.65 / 100.
this gives me 0.0765, but I want just .0765.
If I take 0.0765 and use a split on "." and use length ect..
I actually get for the array [1] a length of 6 and a value of 076500.
Again I only want .0765 or just 0765 and I can add the dot.
Any other ideas that I have not tried?
This will eventually need to be a string since I am passing it in as a prama into SSRS.

You should be able to use a format to create the string:
var taxRateDecimal = 0.0765D;
var reportParameter = taxRateDecimal.ToString(".0000", CultureInfo.InvariantCulture);
The resulting reportParameter is .0765.
Other results for that format are:
0D -> .0000
1D -> 1.0000
1.23456D -> 1.2346
You have to use CultureInfo.InvariantCulture to be sure that the decimal separator is a dot. Otherwise the current culture (which is the default) might specify a comma as the decimal separator.

string.Format will handle this easily.
double taxRateDecimal = 1.0765;
string formattedResult = string.Format("{0:.0000}", taxRateDecimal % 1);
Console.WriteLine(formattedResult); // .0765

How to change 1 to 00001?

I want to have numbers with a fixed digit count.
example: 00001, 00198, 48484
I can do like this:
string value;
if (number < 10)
{
value = "0000" + number.ToString();
}
else if (number < 100)
{
value = "000" + number.ToString();
}
else if (number < 1000)
{
...
}
But this is a bit odd. Is there any built in function for my purpose?

Yes, there is:
string value = String.Format("{0:D5}", number);

According to the MS reference: http://msdn.microsoft.com/en-us/library/dd260048.aspx
You can pad an integer with leading zeros by using the "D" standard
numeric format string together with a precision specifier. You can pad
both integer and floating-point numbers with leading zeros by using a
custom numeric format string.
So:
To display the integer as a decimal value, call its ToString(String)
method, and pass the string "Dn" as the value of the format parameter,
where n represents the minimum length of the string.
Code:
string value = number.ToString("D5");
.NET fiddle: http://dotnetfiddle.net/0U9A6N

You should use the ToString() method with custom formating - see the docs. In particular the 0 specifier.
Replaces the zero with the corresponding digit if one is present; otherwise, zero appears in the result string.
eg,
value = number.Tostring("00000");

string value = number.ToString("00000");

You can do it this way :
number.ToString("00000")

If you wish to return 5 digits numbers, you should use the PadLeft() function;
int Value = 101;
char pad = '0';
String sValue = Value.ToString();
sValue = sValue.s.PadLeft(5, char)
In this case, you don't have to test whether to add 1, 2 or 3 zeros, it'll automatically add the number of zeros needed to make it 5 digits number.

int input_number = Convert.ToInt32(txtinput.Text);
string number_value = input_number.ToString("00000");
I hope that it will solve your problem. It worked well for me in my previous project.
Test this code in your development. It should be worked properly without doubt.

Same as #Jojo's answer, but using C# 6's interpolated strings:
var value = $"{number:00000}";

Apart from String.Format, You can also use String.PadLeft
value = number.ToString().PadLeft(5, '0');

Convert.ToInt32() conditional formatting according to string with comma

string str = e.Row.Cells[index].Text;
int value = Int32.Parse(str, NumberStyles.AllowThousands, NumberFormatInfo.InvariantInfo);
if (value >= 100)
e.Row.Cells[index].BackColor = System.Drawing.Color.Green;
Cell values are 168,88 - 125,45 - 75,3
After parsing str returns 16888 - 12545 - 753 , so all of the cells are set as green
how can i compare real values.?

You are using NumberFormatInfo.InvariantInfo. This treats , as thousands separator.
Are you sure this is the correct one? Did you mean to use something like CultureInfo.GetCulture("fr-FR"), where the , is the decimal separator?
Additionally, if you need to preserve the decimal part, why parse to an integer?
This should work better for you:
decimal.Parse(str, NumberStyles.AllowThousands, CultureInfo.GetCulture("fr-FR"));

I think what you're looking for is:
int value = Int32.Parse(str, NumberStyles.AllowThousands, NumberFormatInfo.CurrentInfo);
The NumberFormatInfo tells the Parse function HOW the input should be interpreted. The InvariantInfo reads as Gets the default read-only NumberFormatInfo that is culture-independent (invariant) from msdn.

How to round and format a decimal correctly? [duplicate]

This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
c# - How do I round a decimal value to 2 decimal places (for output on a page)
I'm trying to get my decimals to display with four decimal places. The DB rounds my number to 4 decimal places, but it returns the number with trailing 0s (due to the decimal precision of the field), so something like 9.45670000. Then, when I do this:
string.Format("{0:#,#.####}", decimalValue);
The output I get on the page is 9.4567, which is what I want.
However, if the number returned from DB is 9.45600000, the output after doing the format is 9.456
But what I need to display is 9.4560
How do I format my decimal, so that the number of decimal places is always four?
UPDATE: Also, is it possible to use a variable (instead of .0000) if I wanted the number of decimal places to be determined dynamically?

string.Format("{0:N4}",decimalValue);
Standard Numeric Format Strings
Custom Numeric Format Strings
To set the precision dynamically you can do the following:
double value = 9.4560000;
int precision = 4;
string format = String.Format("{{0:N{0}}}",precision);
string valuestring = String.Format(format, value);

string.Format({0:#,#0.0000}, decimalValue);

Use String.Format -
decimal d =123.47
string specifier="{0:0,0.0000}"; // You need to get specifier dynamically here..
String.Format(specifier, d); // "123.4700"

Try this:
string.Format("{0:#,###.0000}", 9.45600000);
Adding the zeroes in the format forces a zero to be output if there is not a digit to put there.
To add the zeroes with the number of zeroes driven programmatically you could do this:
int x = 5;
string fmt = "{0:#,###." + new string('0', x) + "}";
string.Format(fmt, 9.456000000);