Format Strings Explained with ASP.NET 4.0 and C#

What is a Format String?
Format strings are used to format common data types when converting them to strings. An example of this would be converting some data in an integer to a string in the format of currency. The standard numeric format strings allow us to convert numeric data to the following formats:

Name	Format Specifier
Currency	C
Decimal	D
Exponential	E
Fixed-point	F
General	G
Number	N
Percent	P
Round-trip	R
Hexadecimal	X

Furthermore, there are also format strings for other types such as dates and times. Some of the datetime formats are as follows:

Format Pattern	Format Specifier
Short Date	d
Long Date	D
Full Date Time	F
Month Day	M
Short Time	t
Long Time	T
Month Year	Y

The Syntax
Let's take a look at an example in which we will convert an integer to a string with the formatting of our currency:

int intData = 123456;
//Output currency
Response.Write(intData.ToString("C"));
Response.Write("<br/>"); //new line

This code will output '$123,456.00'. Notice the syntax that we use for the format string. We simply call the ToString method, pass it the format specifier, and it does the rest for us.


Let's take a look at an example where we want to ouput a double as a string with only a specified number of decimal places:

double dblData = 12345.6789;
//Output fixed-point to specific precision

Response.Write(dblData.ToString("F3"));
Response.Write("<br/>"); //new line

This code will output '12345.679'. Notice, to specify the number of decimals places we simply just need to append a number to the format specifier.