Language Fundamentals in brief C# - Introduction

Language Fundamentals in brief

C# - Introduction

C#

All program logic must be embedded in (typically) a class. Every executable program must contain a Main-method. The Main-method is the starting point of the application.C# is case-sensitiveNo multiple inheritance (only between interfaces) All classes inherit object Garbage-collectionC# supports operator and method overloading

A class

public class Book{

private string title;private string author;public Book(string t, string a) //Constructor{ title= t; author= a;}public override string ToString(){ return (title+" "+author);}

}

Driver Program (Main)

public class BookMain{ public static void Main() {

Book b1= new Book("C#","Troelsen");Book b2= new Book("Java","Kölling");

System.Console.WriteLine(b1.ToString());System.Console.WriteLine(b2);

}}

C#- Namespaces and Using

Namespaces is a tool for structuring programs and systemsMakes it possible to use the same names (identifiers) in different parts of an application.Namespaces may be nestedVisual Studio creates default a namespace with the same name as the projectusing <namespace name> tells the compiler where to look for definitions that our program refers toNamespaces are not the same as Java-packages, but they are used for the same things and there are similarities

C#- value- and reference-types

Objects of value-type are stack allocated – objects of reference type are allocated on the heapValue types die, when control goes out of the scope, where they are declared – reference types are removed by the garbage collectorValue types are copied with assignment – with reference types a reference (the address) is copied

C#- reference types - example

creation, assignment and comparison:

Customer c1, c2, c3;string s1, s2;

c1 = new Customer("Flemming Sander", 36259);c2 = new Customer(”Bjarne Riis", 55298);c3 = null; // c3 refers to nothing

c3 = c1; // c3 refers to the same object as c1

if (c1 == null) ... // is c1 referring to something? if (c1 == c2) ... // compare references if (c1.Equals(c2)) ... // compares object-values

C#- When are objects equal?

Classes ought to override the Equals-methodpublic class Customer{ . . .

public override bool Equals(object obj) { Customer other; if ((obj == null) || (!(obj is Customer))) return false; // surely not equal

other = (Customer) obj; // explicit typecast return this.id == other.id; // equal if ids are... }}

C#- Boxing and Unboxing

C# converts automatically between simple value and object

value => object = "boxing“ (the value is “wrapped in a box”)object => value = "unboxing“ (the value is unwrapped again)

int i, j;object obj;string s;

i = 32;obj = i; // boxing (copy)i = 19;j = (int) obj; // unboxing!

s = j.ToString(); // boxing!s = 99.ToString(); // boxing!

C#- arrays

Arrays are reference typesCreated from the Array-class in FCLCreated using the new-operator0-based indexingAre initialised with default value (0 if numeric, null if reference)

int[] a;a = new int[5];

a[0] = 17;a[1] = 32;int x = a[0] + a[1] + a[4];

int l = a.Length;

Access element 1

Creation

Number of elements

C#- structs

In some ways like a class, but there are differences:

Can have instance variables and methodsCannot have a default constructorVariables of a struct-type are value types and as such stack allocatedCan only inherit from interfacesCannot be inherited from

Can be used to implement ADTs (Abstract Data Type), but no inheritance and polymorphism

C#- selection and iteration

x = obj.foo();

if (x > 0 && x < 10) count++;else if (x == -1) ...else { ...}

while (x > 0){ ...

x--;} for (int k = 0; k < 10; k++)

{ ...}

C#- foreach-loop

foreach loop is used to sweep over collections as arrays

Reduces the risk of indexing errors

int[] data = { 1, 2, 3, 4, 5 };int sum = 0;

foreach (int x in data){ sum += x;}

foreach

type value collection

C#- Methods

A class may have two kind of methods:Instance methodsStatic methods (class methods)Instance methods need an object to be invokedStatic methods are called using the class name only

C#- Example

The array-class in BCL (FCL)The class is a member of namespace System (System.Array)

namespace System{ public class Array { public int GetLength(int dimension) { ... }

public static void Sort(Array a) { ... }

. . .

}}

instance method

static method

C#- calling the methods

/* main.cs */

using System;

public class App{ public static void Main() { int[] data = { 11, 7, 38, 55, 3 }; Array.Sort(data);

for (int i=0; i<data.GetLength(0); i++) Console.WriteLine(i + ": " + data[i]); }}

Class-method Instance-method