četvrtak, 18.09.2008.

C# Collections

Collections are similar to arrays: they store lists of objects. Hwever they provide a lot of usefull features not found in arrays (resizing, sorting etc). Microsoft .Net Framework provides severaltypes of collection classes_


  • ArrayList Class -similar to array

    • Remove method - removes an element

    • Add method - adds a new element at the end

    • Insert method - inserts a new element somewhere in the middle



  • Stack Class - implements LIFO mechanism - like a stack

    • Push - adds an element at the beginning

    • Pop - removes an element from the end



  • Hashtable Class - associative array - using other data types as element key

    • ContainsKey - ckeck if the key is already taken

    • elements are stored in DictionaryEntry object - used in foreach loop



  • SortedList Class - similar to Hashtable - elements allways sorted (by using key)



Collections and arrays use similar syntax: elements can be added to collection in the following way:

SortedList peopleAge = new SortedList();
peopleAge["john"] = 31;
peopleAge["mary"] = 36;
peopleAge["James"] = 53;
peopleAge["Francesca"] = 18;


Iteration is done the same way as in arrays, with the difference that items are returned as DictionaryEntry, meaning that casting needs to be used.

- 20:48 - Komentari (0) - Isprintaj - #

C# Arrays

C# arrays are similar to ones in C/C++:


  • zero based

  • stored on heap (not stack)

  • square brackets [] are used in their declaration

  • once declared, their size can't be changed



However in addition to that, they have some extra features (some inherated from System.Array class):

  • Length property which returns the size of an array

  • methods for copying arrays in one go



How to declare an array:

int[] myNewArray; // uninitialized array variable of int type
int[] myNewArray = new int[15]; // declaring a variable and initializing array of 15 elements (they are initialized to 0 by default)
int[] myNewArray = {9, 3, 7, 2}; // creating and initializing an array at the same time - it's size is 4 = the number of elements


How to iterate through an array & access array elements:
There are two ways: the traditional for loop:

for(int iIndex=0; iIndex {
Console.WriteLine(myNewArray[iIndex]);
}

and the new foreach loop:

foreach(int arrayElement in myNewArray)
{
Console.WriteLine(arrayElement);
}


How to copy an array:

// The First way of copying arrays - using CopyTo method
int[] sourceArray = {9, 3, 7, 2};
int[] targetArray = new int[sourceArray.Length]; // target array must be exactly the same size

sourceArray.CopyTo(targetArray, 0); // 0 is the starting index

// The Second way of copying arrays - using Array.Copy method
int[] sourceArray = {9, 3, 7, 2};
int[] targetArray = new int[sourceArray.Length]; // target array must be exactly the same size

Array.Copy(sourceArray, targetArray, targetArray.Length);

// The Second way of copying arrays - using Clone method
int[] sourceArray = {9, 3, 7, 2};
int[] targetArray =(int[]) sourceArray.Clode(); // Clone returns object data type, so casting is required


All these three methods use "shallow" copying, meaning that if copying an array of object references, only the references will be copied and not the objects they are reffering to.

Arrays are fine for simple stuff. For more complicated things there are collections... which will be explained later

- 20:20 - Komentari (0) - Isprintaj - #

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