WriteLine formatting in C#



WriteLine is used to output a line of string in C#. It is often required to output a integer, string or other variable in a certain way. We need to use formatting in such cases.
The format parameter in formatting is embedded with zero or more format specifications of the form "{ N [, M ][: formatString ]}", arg1, ... argN, where:
* N is a zero-based integer indicating the argument to be formatted.
* M is an optional integer indicating the width of the region to contain the formatted value, padded with spaces. If M is negative, the formatted value is left-justified; if M is positive, the value is right-justified.
* formatString is an optional string of formatting codes.
* argN is the expression to use at the equivalent position inside the quotes in the string.
Consider the following example to understand it 


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
	
	Console.WriteLine("{0,5} {1,5}", 123, 456);      // Right-aligned
	Console.WriteLine("{0,-5} {1,-5}", 123, 456);    // Left-aligned
	Console.WriteLine("{0,-10:D6} {1,-10:D6}", 123, 456); // D6 means 6 decimal digits
        Console.ReadLine();


        }
    }
}
If you run the above program you should be able to see an output something similar to 

	
  123  456
123  456
000123     000456


Format Specifiers


Standard numeric format strings are used to return strings in commonly used formats. They take the form X0, in which X is the format specifier and 0 is the precision specifier. The format specifier can be one of the nine built-in format characters that define the most commonly used numeric format types, as shown in Table 10-1.

Table 10-1 - String and WriteLine Format Specifiers

Character

Interpretation

C or c

Currency

D or d

Decimal (decimal integer—don’t confuse with the .NET Decimal type)

E or e

Exponent

F or f

Fixed point

G or g

General

N or n

Currency

P or p

Percentage

R or r

Round-trip (for floating-point values only); guarantees that a numeric value converted to a string will be parsed back into the same numeric value

X or x

Hex




using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
	
        int i = 123456;
        Console.WriteLine("{0:C}", i); // $123,456.00
        Console.WriteLine("{0:D}", i); // 123456
        Console.WriteLine("{0:E}", i); // 1.234560E+005
        Console.WriteLine("{0:F}", i); // 123456.00
        Console.WriteLine("{0:G}", i); // 123456
        Console.WriteLine("{0:N}", i); // 123,456.00
        Console.WriteLine("{0:P}", i); // 12,345,600.00 %
        Console.WriteLine("{0:X}", i); // 1E240
        Console.ReadLine();


        }
    }
}


If you run above you should see the following command 


$123,456.00
123456
1.234560E+005
123456.00
123456
123,456.00
12,345,600.00 %
1E240


If the standard formatting specifiers aren’t enough for you, you can use picture format strings to create custom string output. Picture format definitions are described using placeholder strings that identify the minimum and maximum number of digits used, the placement or appearance of the negative sign, and the appearance of any other text within the number, as shown in Table 10-2.

Table 10-2 - Custom Format Specifiers

Format Character

Purpose

Description

0

Display zero placeholder

Results in a nonsignificant zero if a number has fewer digits than there are zeros in the format

#

Display digit placeholder

Replaces the pound symbol (#) with only significant digits

.

Decimal point

Displays a period (.)

,

Group separator

Separates number groups, as in 1,000

%

Percent notation

Displays a percent sign (%)

E+0
E-0
e+0
e-0

Exponent notation

Formats the output of exponent notation

\

Literal character

Used with traditional formatting sequences such as “\n” (newline)

'ABC'
"ABC"

Literal string

Displays any string within quotes or apostrophes literally

;

Section separator

Specifies different output if the numeric value to be formatted is positive, negative, or zero

Let’s see the strings that result from a set of customized formats, using first a positive integer, then using the negative value of that same integer, and finally using zero:

The example below shows the results in comments based upon the format specifier. 


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
	
int i = 123456;
Console.WriteLine();
Console.WriteLine("{0:#0}", i);             // 123456

Console.WriteLine("{0:#0;(#0)}", i);        // 123456

Console.WriteLine("{0:#0;(#0);}", i); // 123456

        Console.WriteLine("{0:#%}", i);     // 12345600%


i = -123456;
Console.WriteLine();
Console.WriteLine("{0:#0}", i);             // -123456

Console.WriteLine("{0:#0;(#0)}", i);        // (123456)

Console.WriteLine("{0:#0;(#0);}", i); // (123456)

Console.WriteLine("{0:#%}", i);             // -12345600%


i = 0;
Console.WriteLine();
Console.WriteLine("{0:#0}", i);             // 0

Console.WriteLine("{0:#0;(#0)}", i);        // 0

Console.WriteLine("{0:#0;(#0);}", i); // 

Console.WriteLine("{0:#%}", i);             // %

Console.ReadLine();
        }
    }
}

This completes your understanding of formatting in C#. You like to experiment on your own to further strengthen your understanding of WriteLine formatting. We will use WriteLine formatting to understand some aspects of C# in next few chapters.