C# – String format for Double

using System;
 
public class Program
{
  public static void Main(string[] args)
    {
        // Pattern 1: just two decimal places
        Console.WriteLine("**************************************");
        Console.WriteLine("Pattern 1: just two decimal places");
        Console.WriteLine("**************************************");
        Console.WriteLine(String.Format("{0:0.00}", 123.4567));      // "123.46"
        Console.WriteLine(String.Format("{0:0.00}", 123.4));         // "123.40"
        Console.WriteLine(String.Format("{0:0.00}", 123.0));         // "123.00"
 
        //Pattern 2: max. two decimal places
        Console.WriteLine("**************************************");
        Console.WriteLine("Pattern 2: max. two decimal places");
        Console.WriteLine("**************************************");
        Console.WriteLine(String.Format("{0:0.##}", 123.4567));      // "123.46"
        Console.WriteLine(String.Format("{0:0.##}", 123.4));         // "123.4"
        Console.WriteLine(String.Format("{0:0.##}", 123.0));         // "123"
 
        //Pattern 3: at least two digits before decimal point
        Console.WriteLine("***************************************************");
        Console.WriteLine("Pattern 3: at least two digits before decimal point");
        Console.WriteLine("***************************************************");
        Console.WriteLine(String.Format("{0:00.0}", 123.4567));      // "123.5"
        Console.WriteLine(String.Format("{0:00.0}", 23.4567));       // "23.5"
        Console.WriteLine(String.Format("{0:00.0}", 3.4567));        // "03.5"
        Console.WriteLine(String.Format("{0:00.0}", -3.4567));       // "-03.5"
 
        //Pattern 4: Thousand Separators
        Console.WriteLine("**************************************");
        Console.WriteLine("Pattern 4: Thousand Separators");
        Console.WriteLine("**************************************");
        Console.WriteLine(String.Format("{0:0,0.0}", 12345.67));     // "12,345.7"
        Console.WriteLine(String.Format("{0:0,0}", 12345.67));       // "12,346"
 
        //Pattern 5: Align Number with spaces
        Console.WriteLine("**************************************");
        Console.WriteLine("Pattern 5: Align Number with spaces");
        Console.WriteLine("**************************************");
        Console.WriteLine(String.Format("{0,10:0.0}", 123.4567));    // "     123.5"
        Console.WriteLine(String.Format("{0,-10:0.0}", 123.4567));   // "123.5     "
        Console.WriteLine(String.Format("{0,10:0.0}", -123.4567));   // "    -123.5"
        Console.WriteLine(String.Format("{0,-10:0.0}", -123.4567));  // "-123.5    "
 
       //Pattern 6: Numbers between zero and one
        Console.WriteLine("**************************************");
        Console.WriteLine("Pattern 6: Numbers between zero and one");
        Console.WriteLine("**************************************");
        Console.WriteLine(String.Format("{0:0.0}", 0.0));            // "0.0"
        Console.WriteLine(String.Format("{0:0.#}", 0.0));            // "0"
        Console.WriteLine(String.Format("{0:#.0}", 0.0));            // ".0"
        Console.WriteLine(String.Format("{0:#.#}", 0.0));            // ""     
 
      //Pattern 7: Custom formatting for negative numbers and zero
        Console.WriteLine("**********************************************************");
        Console.WriteLine("Pattern 7: Custom formatting for negative numbers and zero");
        Console.WriteLine("**********************************************************");
        Console.WriteLine(String.Format("{0:0.00;minus 0.00;zero}", 123.4567));   // "123.46"
        Console.WriteLine(String.Format("{0:0.00;minus 0.00;zero}", -123.4567));  // "minus 123.46"
        Console.WriteLine(String.Format("{0:0.00;minus 0.00;zero}", 0.0));        // "zero"
    }
}

Kaynak