C#- Collection

We had posted about  array before. however C# also includes specialized classes that hold many values or objects in a specific series, that are called ‘collection’.
There are two types of collections available in C#: non-generic collections and generic collections.and now we are going to learn about non-generic collections

Every collection class implements the IEnumerable interface so values from the collection can be accessed using a foreach loop.

The System.Collections namespace includes following non-generic collections.

Non-generic Collections Usage
ArrayList ArrayList stores objects of any type like an array. However, there is no need to specify the size of the ArrayList like with an array as it grows automatically.
SortedList SortedList stores key and value pairs. It automatically arranges elements in ascending order of key by default. C# includes both, generic and non-generic SortedList collection.
Stack Stack stores the values in LIFO style (Last In First Out). It provides a Push() method to add a value and Pop() & Peek() methods to retrieve values. C# includes both, generic and non-generic Stack.
Queue Queue stores the values in FIFO style (First In First Out). It keeps the order in which the values were added. It provides an Enqueue() method to add values and a Dequeue() method to retrieve values from the collection. C# includes generic and non-generic Queue.
Hashtable Hashtable stores key and value pairs. It retrieves the values by comparing the hash value of the keys.
BitArray BitArray manages a compact array of bit values, which are represented as Booleans, where true indicates that the bit is on (1) and false indicates the bit is off (0).

we will take the above one by one and learn more about them in the next couple of blog posts :).

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C# – Array

An array is a special type of data type which can store fixed number of values sequentially using special syntax.

The following image shows how an array stores values sequentially.


 

As you can see in the above figure, index is a number starting from 0, which stores the value. You can store a fixed number of values in an array. Array index will be increased by 1 sequentially till the maximum specified array size.

Array Declaration

An array can be declare using a type name followed by square brackets [].

Example: Array declaration in C#
int[] intArray; // can store int values
bool[] boolArray; // can store boolean values

string[] stringArray; // can store string values

double[] doubleArray; // can store double values
byte[] byteArray; // can store byte values
Courses[] customClassArray; // can store instances of Courses class

Initialization

An array can be declared and initialized at the same time using the new keyword. The following example shows the way of initializing an array.

Example: Array Declaration & Initialization
// defining array with size 5. add values later on
int[] intArraySample1 = new int[5]; 
// defining array with size 5 and adding values at the same time
int[] intArraySample2 = new int[5]{1, 2, 3, 4, 5};
// defining array with 5 elements which indicates the size of an array
int[] intArraySample3 = {1, 2, 3, 4, 5};

In the above example, the first statement declares & initializes int type array that can store five int values. The size of the array is specified in square brackets. The second statement, does the same thing, but it also assignes values to each indexes in curley brackets { }. The third statement directly initializes an int array with the values without giving any size. Here, size of an array will automatically be number of values.

Initialization without giving size is NOT valid. For example, the following example would give compile time error.

Example: Wrong way of initializing an array
int[] intArray = new int[]; // compiler error: must give size of an array

Late initialization

Arrays can be initialized after declaration. It is not necessary to declare and initialize at the same time using new keyword. Consider the following example.

Example: Late initialization of an Array
string[] strArray1, strArray2;

strArray1 = new string[5]{ "1st Element",
                           "2nd Element", 
                           "3rd Element",
                           "4th Element",
                           "5th Element" 
                          };


strArray2 = new string[]{ "1st Element",
                           "2nd Element",
                           "3rd Element",
                           "4th Element", 
                           "5th Element" 
                          };

However, in the case of late initialization, it must be initialized with the new keyword as above. It cannot be initialize by only assigning values to the array.

The following initialization is NOT valid:

Example: Wrong way of initializing an array
string[] strArray;

strArray = {"1st Element","2nd Element","3rd Element","4th Element" };

Accessing Array Elements

As shown above, values can be assigned to an array at the time of initialization. However, value can also be assigned to individual index randomly as shown below.

Example: Assigning values to array index
int[] intArray = new int[5];
intArray[0] = 10;
intArray[1] = 20;
intArray[2] = 30;
intArray[3] = 40;
intArray[4] = 50;

In the same way, you can retrieve values at a particular index, as below:

Example: Accessing Array elements

intArray[0];  //returns 10
intArray[2];  //returns 30

Use a for loop to access the values from all the indexes of an array by using length property of an array.

Example: Accessing Array elements using for loop
int[] intArray = new int[5]{10, 20, 30, 40, 50 };

for(int i = 0; i < intArray.Length; i++)
    Console.WriteLine(intArray[i]);   
10 
20
30
40
50

Array properties and methods

Method Name Description
GetLength(int dimension) Returns the number of elements in the specified dimension.
GetLowerBound(int dimension) Returns the lowest index of the specified dimension.
GetUpperBound(int dimension) Returns the highest index of the specified dimension.
GetValue(int index) Returns the value at the specified index.
Property Description
Length Returns the total number of elements in the array.

Array Helper Class

.NET provides an abstract class, Array, as a base class for all arrays. It provides static methods for creating, manipulating, searching, and sorting arrays.

For example, use the Array.Sort() method to sort the values:

Example: Array Helper class
int[] intArr = new int[5]{ 2, 4, 1, 3, 5};

Array.Sort(intArr);

Array.Reverse(intArr);

You can create an instance of an Array that starts with index 1 (not default starting index 0) using Array class as shown below:

Example: Array Helper class
Array array = Array.CreateInstance(typeof(int),new int[1]{5},new int[1]{1});

array.SetValue(1, 1);
array.SetValue(2, 2);
array.SetValue(3, 3);
array.SetValue(4, 4);
array.SetValue(5, 5);

for (int i = 1; i <= array.Length; i++)
    Console.WriteLine("Array value {0} at position {1}", array.GetValue(i), i);
Output:

Array value 1 at position 1
Array value 2 at position 2
Array value 3 at position 3
Array value 4 at position 4
Array value 5 at position 5

 never forget  :
  1. An Array stores values in a series starting with a zero-based index.
  2. The size of an array must be specified while initialization.
  3. An Array values can be accessed using indexer.
  4. An Array can be single dimensional, multi-dimensional and jagged array.
  5. The Array helper class includes utility methods for arrays.
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C# Variable

Example: C# Variable

namespace CSharpTutorials
{
    class Program
    {
        static void Main(string[] args)
        {
            string message = "Hello World!!";

            Console.WriteLine(message);
        }
    }
}

The variable in C# is nothing but a name given to a data value. In the above example, message is the name of the variable that stores the string data value “Hello World!!”. As the name suggests, the contents of a variable can vary, i.e., you can change the value of a variable at any time.

In C#, a variable is always defined with a data type. The following is the syntax variable declaration and initialization.

Variable Syntax:
<data type> <variable name>;

<datatype> <variable name> = <value>;

A variable can be declared and initialized later or it can be declared and initialized at the same time. In the following example, the first statement declares a variable called “message” without assigning any value to it. In the second statement, a value is assigned to the “message” variable.

Example: Variable Declaration
string message;

// value can be assigned after it declared 
message = "Hello World!!";

In the following example, variable is declared and initialized (a value is assigned to it) at the same time.

Example: Variable Declaration & Initialization
string message = "Hello World!!";

Multiple variables of the same data type can be declared and initialized in a single line separated by commas.

Example: Multiple Declarations
int i, j, k, l = 0;

int amount, num;

When declaring multiple variables of the same data type, you can put them in multiple lines for the sake of readability; even if split across multiple lines, the compiler will consider it to be one statement, until it encounters a semicolon (;).

Example: Multi-Line Declarations
int i, j, 
    k, 
    l = 0;

The value of a variable can be assigned to another variable of the same data type. However, a value must be assigned to a variable before using it.

Example: Variable Assignment
int i = 100;

int j = i; // value of j will be 100

The following example would give a compile time error because string value cannot be assinged to a int type variable.

Example: Invalid Variable Assignment
string message = "Hello World!!";

int i = message; // compile time error

You must assign a value to a variable before using it otherwise the compiler will give an error. For example, in the following code, we have declared a variable called i without assigning any value to it. If we then try to display the value of the variable on the console, we will get a compile time error.

Example: Invalid Variable Assignment
int i;

//Following will give compile time error: "Use of unassigned local variable 'i'"
int j = i;
Console.WriteLine(j); 
 Points to Remember :
  1. The variable is a name given to a data value.
  2. A variable holds the value of specific data type e.g string, int, float etc.
  3. A variable can be declared and initialized in separate statements and also in the single statement.
  4. The value of a variable can be changed at any time throught out the program as long as it is accessible.
  5. Multiple variables can be defined seperated by comma (,) in a single or multiple line till semicolon(;).
  6. A value must be assigned to a variable before using it otherwise it will give compile time error.
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C# Access modifiers

Access modifiers are applied on the declaration of the class, method, properties, fields and other members. They define the accessibility of the class and its members.

Access Modifiers Usage
public The Public modifier allows any part of the program in the same assembly or another assembly to access the type and its members.
private The Private modifier restricts other parts of the program from accessing the type and its members. Only code in the same class or struct can access it.
internal The Internal modifier allows other program code in the same assembly to access the type or its members. This is default access modifiers if no modifier is specified.
protected The Protected modifier allows codes in the same class or a class that derives from that class to access the type or its members.
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C# Version History

C# is a simple & powerful object-oriented programming language developed by Microsoft.

C# has evolved much since its first release in 2002. C# was introduced with .NET Framework 1.0 and the current version of C# is 6.0.

The following table lists important features introduced in each version of C#:

Version Important Features
C# 1.0
  • Basic features
C# 2.0
  • Generics
  • Partial types
  • Anonymous methods
  • Iterators
  • Nullable types
  • Private setters (properties)
  • Method group conversions (delegates)
  • Covariance and Contra-variance
  • Static classes
C# 3.0
  • Implicitly typed local variables
  • Object and collection initializers
  • Auto-Implemented properties
  • Anonymous types
  • Extension methods
  • Query expressions
  • Lambda expressions
  • Expression trees
  • Partial Methods
C# 4.0
  • Dynamic binding (late binding)
  • Named and optional arguments
  • Generic co- and contravariance
  • Embedded interop types
C# 5.0
  • Async features
  • Caller information
C# 6.0
  • Expression Bodied Methods
  • Auto-property initializer
  • nameof Expression
  • Primary constructor
  • Await in catch block
  • Exception Filter
  • String Interpolation
C# 7.0
  • out variables
  • Tuples
  • Discards
  • Pattern Matching
  • Local functions
  • Generalized async return types
  • throw Expressions
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C# – Get Started

C# is an elegant and type-safe object-oriented language that enables developers to build a variety of secure and robust applications that run on the .NET Framework. You can use C# to create Windows client applications, XML Web services, distributed components, client-server applications, database applications, and much, much more. Visual C# provides an advanced code editor, convenient user interface designers, integrated debugger, and many other tools to make it easier to develop applications based on the C# language and the .NET Framework.

And here in developersportal.net we are going to post a C# tutorials that will help you learn the essentials of C#, from the basic to advance level topics.

These tutorials are designed for beginners and professionals who want to learn C# step-by-step.

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