http://www.demo2s.com/Code/CSharp/Development-Class/Usingcustomformats.htm

/*
C#: The Complete Reference
by Herbert Schildt

Publisher: Osborne/McGraw-Hill (March 8, 2002)
ISBN: 0072134852
*/


// Using custom formats.

using System;

public class PictureFormatDemo {
public static void Main() {
double num = 64354.2345;

Console.WriteLine("Default format: " + num);

// Display with 2 decimal places.
Console.WriteLine("Value with two decimal places: " +
"{0:#.##}", num);

// Display with commas and 2 decimal places.
Console.WriteLine("Add commas: {0:#,###.##}", num);

// Display using scientific notation.
Console.WriteLine("Use scientific notation: " +
"{0:#.###e+00}", num);

// Scale the value by 1000.
Console.WriteLine("Value in 1,000s: " +
"{0:#0,}", num);

/* Display positive, negative, and zero
values differently. */
Console.WriteLine("Display positive, negative, " +
"and zero values differently.");
Console.WriteLine("{0:#.#;(#.##);0.00}", num);
num = -num;
Console.WriteLine("{0:#.##;(#.##);0.00}", num);
num = 0.0;
Console.WriteLine("{0:#.##;(#.##);0.00}", num);

// Display a percentage.
num = 0.17;
Console.WriteLine("Display a pecentage: {0:#%}", num);
}
}