Csharp/CSharp Tutorial/Class/IFormattable

Formattable Vector

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

class MainEntryPoint {
    static void Main() {
        Vector v1 = new Vector(1, 32, 5);
        Vector v2 = new Vector(845.4, 54.3, -7.8);
        Console.WriteLine("{0,30:IJK}   \n   {1,30:IJK} \n", v1, v2);
        Console.WriteLine("{0,30}       \n   {1,30} \n", v1, v2);
        Console.WriteLine("{0,30:VE}    \n   {1,30:VE} \n", v1, v2);
        Console.WriteLine("{0,20:N}     \n   {1,20:N}", v1, v2);
    }
}
struct Vector : IFormattable {
    public double x, y, z;
    public Vector(double x, double y, double z) {
        this.x = x;
        this.y = y;
        this.z = z;
    }
    public string ToString(string format, IFormatProvider formatProvider) {
        if (format == null)
            return ToString();
        string formatUpper = format.ToUpper();
        switch (formatUpper) {
            case "N":
                return "|| " + Norm().ToString() + " ||";
            case "VE":
                return String.Format("( {0:E}, {1:E}, {2:E} )", x, y, z);
            case "IJK":
                StringBuilder sb = new StringBuilder(x.ToString(), 30);
                sb.Append(" i + ");
                sb.Append(y.ToString());
                sb.Append(" j + ");
                sb.Append(z.ToString());
                sb.Append(" k");
                return sb.ToString();
            default:
                return ToString();
        }
    }
    public Vector(Vector rhs) {
        x = rhs.x;
        y = rhs.y;
        z = rhs.z;
    }
    public override string ToString() {
        return "( " + x + " , " + y + " , " + z + " )";
    }
    public double this[uint i] {
        get {
            switch (i) {
                case 0:
                    return x;
                case 1:
                    return y;
                case 2:
                    return z;
                default:
                    throw new IndexOutOfRangeException(
                       "Attempt to retrieve Vector element" + i);
            }
        }
        set {
            switch (i) {
                case 0:
                    x = value;
                    break;
                case 1:
                    y = value;
                    break;
                case 2:
                    z = value;
                    break;
                default:
                    throw new IndexOutOfRangeException(
                       "Attempt to set Vector element" + i);
            }
        }
    }
    private const double Epsilon = 0.0000001;
    public static bool operator ==(Vector lhs, Vector rhs) {
        if (System.Math.Abs(lhs.x - rhs.x) < Epsilon &&
           System.Math.Abs(lhs.y - rhs.y) < Epsilon &&
           System.Math.Abs(lhs.z - rhs.z) < Epsilon)
            return true;
        else
            return false;
    }
    public static bool operator !=(Vector lhs, Vector rhs) {
        return !(lhs == rhs);
    }
    public static Vector operator +(Vector lhs, Vector rhs) {
        Vector Result = new Vector(lhs);
        Result.x += rhs.x;
        Result.y += rhs.y;
        Result.z += rhs.z;
        return Result;
    }
    public static Vector operator *(double lhs, Vector rhs) {
        return new Vector(lhs * rhs.x, lhs * rhs.y, lhs * rhs.z);
    }
    public static Vector operator *(Vector lhs, double rhs) {
        return rhs * lhs;
    }
    public static double operator *(Vector lhs, Vector rhs) {
        return lhs.x * rhs.x + lhs.y + rhs.y + lhs.z * rhs.z;
    }
    public double Norm() {
        return x * x + y * y + z * z;
    }
}

Implementation of IFormattable

using System;
public class MyClass : IFormattable
{
    private string title;
    private string[] names;
    public MyClass(string title, params string[] names)
    {
        this.title = title;
        this.names = names;
    }
    public override string ToString()
    {
        return ToString("G", null);
    }
    public string ToString(string format, IFormatProvider formatProvider)
    {
        string result = null;
        if (format == null) 
            format = "G";
        switch (format.ToUpper()[0])
        {
            case "S":
                result = "S." ;
                break;
            case "P":
                result = "P. ";
                break;
            case "I":
                result = "I. ";
                break;
            case "G":
            default:
                result = "G. ";
                break;
        }
        return result;
    }
}
public class MainClass
{
    public static void Main()
    {
        MyClass person = new MyClass("Mr", "A", "B", "C", "D");
        System.Console.WriteLine("Dear {0:G},", person);
        System.Console.WriteLine("Dear {0:P},", person);
        System.Console.WriteLine("Dear {0:I},", person);
        System.Console.WriteLine("Dear {0},", person);
        System.Console.WriteLine("Dear {0:S},", person);
    }
}

Dear G. ,
Dear P. ,
Dear I. ,
Dear G. ,
Dear S.,

Implements IFormattable with switch statement

using System;

public class Employee : IFormattable {
    private string title;
    private string[] names;
    public Employee(string title, params string[] names) {
        this.title = title;
        this.names = names;
    }
    public override string ToString() {
        return ToString("G", null);
    }
    public string ToString(string format, IFormatProvider formatProvider) {
        string result = null;
        if (format == null) format = "G";
        switch (format.ToUpper()[0]) {
            case "S":
                result = names[0][0] + "." + names[names.Length - 1];
                break;
            case "P":
                if (title != null && title.Length != 0) {
                    result = title + ".";
                }
                break;
            case "I":
                result = names[0];
                break;
            case "G":
            default:
                result = names[0] + " " + names[names.Length - 1];
                break;
        }
        return result;
    }
}
public class MainClass {
    public static void Main() {
        Employee person = new Employee("Mr", "A", "B", "C", "D");
        System.Console.WriteLine("{0:G},", person);
        System.Console.WriteLine("{0:P},", person);
        System.Console.WriteLine("{0:I},", person);
        System.Console.WriteLine("{0},", person);
        System.Console.WriteLine("{0:S},", person);
    }
}