C# Questions

struct vs Class

• structs are value types that can contain data and functions
• structs are value types and do not require heap allocation.
• structs directly store their data in the struct, classes store a reference to a dynamically allocated object.
• structs are useful for small data structures
• structs can affect performance
• Constructors are invoked with the new operator, but that does not allocate memory on the heap
• A struct constructor simply returns the struct value itself (typically in a temporary location on the stack), and this value is then copied as necessary
• With classes, multiple variables may have a reference to the same object
• It is possible for operations on one variable to affect the object referenced by the other variable.
• With structs, the variables each have their own copy of the data, and it is not possible for operations on one to affect the other.
• structs do not support user-specified inheritance, and they implicitly inherit from type object

Public struct PointStruct {  public int x;  public int y;  public PointStruct(int x, int y)  {   this.x = x;   this.y = y;  } } static void Main(string[] args) {  PointStruct ps = new PointStruct();  ps.x = 10;  ps.y = 10;  Console.WriteLine(“Initial struct values are “ + ps.x +”, “+ ps.y);  ModifyStructPoint(ps);  Console.WriteLine(“After ModifyStructPoint, struct values are “ + ps.x +”, “+ ps.y); } void ModifyStructPoint(PointStruct newStruct) {  newStruct.x = 20;  newStruct.y = 20;  Console.WriteLine(“Inside ModifyStructPoint()”);  Console.WriteLine(“Modified values are “ + newStruct.x +”, “+ newStruct.y); } Initial struct values are 10,10 Inside ModifyStructPoint() Modified values are 20,20 After ModifyStructPoint, struct values are 10,10

class PointClass {  public int x;  public int y;  public PointClass(int x, int y)  {  this.x = x;  this.y = y;  } } static void Main(string[] args) {  PointClass pc = new PointClass(10,10);  Console.WriteLine(“Initial class values are “ + pc.x +”, “+ pc.y);  ModifyClassPoint(pc);  Console.WriteLine(“After ModifyClassPoint, class are “ + ps.x +”, “+ ps.y); } void ModifyClassPoint(PointStruct newPoint) {  newPoint.x = 20;  newPoint y = 20;  Console.WriteLine(“Inside ModifyClassPoint()”);  Console.WriteLine(“Modified values are “ + newPoint.x +”, “+ newPoint.y); } Initial class values are 10,10 Inside ModifyClassPoint() Modified values are 20,20 After ModifyClassPoint, struct values are 20,20

Parse XML Files

• Reference System.Xml 
• Use XmlReader to parse the text string 
• XmlReader methods to read the XML data

String xmlString = @”<bookstore><book genre=“autobiography” publications=“…” isbn=“…”><title>this is test</title><author><first>…</first><last>…</last></author></book></bookstroe>”

StringBuilder output = StringBuilder();
using (XmlReader reader = XmlReader.Create(new StringReader(xmlString))
{
 reader.ReadToFollowing(“book”); //read the first element
 reader.MovetoFirstAttribute();
 string genre = reader.value();
 reader.ReadToFollowing(“tittle”) //autobiography
 string titlle = reader.ReadElementContentAsString() //this is test
}

Difference between String and string

• The string type is a sealed class type that inherits directly from object.
• Values of the string type can be written as string literals.
• The keyword string is simply an alias for the predefined class System.String
• Use string for variable names
• Use String for class methods and reference
• Coding conventions state that upper case String should be used for ‘Class methods’
•  typeof(string)  or typeof(String) //System.String

Calling base Constructor in C#

RegEx
RegEx – is powerful string manipulation tool, super fast and efficient
string blog_content = ".net.net test .net .nettest.net .net"'
RegEx.Matches(blog_content, ".net") //6

Difference Between abstract and virtual functions

• Abstract methods have no implementation and MUST be overridden.
• Virtual methods MAY have an implementation but are not required to and then CAN be overridden.
• You cannot call base.method() for abstract but you can for virtual methods

Difference Between ref and out keyword
They're pretty much the same - the only difference is that a variable you pass as an out parameter doesn't need to be initialized

public void RefOut()
{
 //string outstring = "this is old out string";
 string outstring; // it won't throw error
 outmethod(out outstring);
 //string refstring = "this is old ref string";
 string refstring; // it will throw error, because not initialized
 refmethod(ref refstring);
}

void outmethod(out string outstring)
{
 outstring = "this is new out string";
}

void refmethod(ref string refstring)
{
 refstring = "this is new out string";
}

Enum

public enum AuthMethod
{
 FORMS =1,
 WINDOW =2,
 SINGLE =3
}

AuthMethod amf = AuthMethoD.FORMS;
string str = Enum.GetName(trpeof(AuthMethod),amf);
str = AuthMethod.FORMS.toString();