1. Introduction to .NET Florin Olariu
“Alexandru Ioan Cuza”, University of Iași
Department of Computer Science

2. Agenda
Arrays
Demo
Generic list
What’s Next
Interview questions

3. Arrays

4. Arrays Definition Declaring and populating an array
Samples
Declaring and populating an array
Using collection initializers
Retrieving an element from an array
Iterating an array
Using array methods
Best practices
Demo

5. Arrays
Definition

6. Arrays
Definition
Is a fixed-size list of elements that can be accessed using a positional index number

7. Arrays “Salt” 2.21 Red Definition White “Pepper” 3.43 “Onion” 5.01
Is a fixed-size list of elements that can be accessed using a positional index number
Sample:
Red
White
Green
Blue
“Salt” 2.21
“Pepper” 3.43
“Onion” 5.01
“Garlic” 3.20
Notes:
1. In arrays index is “0-based”.
2. Arrays are fixed size.(we will define the size of an array when this is initialized – once is initialized the size cannot be adjusted)

8. Arrays Definition 1 2 3 Red White Green Blue 1 2 3 “Salt” 2.21
Is a fixed-size list of elements that can be accessed using a positional index number
Sample: 1 2 3
Red
White
Green
Blue 1 2 3
“Salt” 2.21
“Pepper” 3.43
“Onion” 5.01
“Garlic” 3.20
Notes:
In arrays index is “0-based”.

9. Arrays
Definition
Samples
Declaring and populating an array

10. Arrays Red Definition White Declaring and populating an array Green
Samples
Declaring and populating an array
Declaring an array:
string[] colors;
Red
White
Green
Blue

11. Arrays Red White Green Blue Definition
Samples
Declaring and populating an array
Declaring an array: Initializing an array:
string[] colors; string[] colors;
colors = new string[4];
string[] colors = new string[4];
var colors = new string[4];
Red
White
Green
Blue
An array is a reference type.
In this case we should use: “new” keyword for initialization.

12. Arrays Definition Declaring and populating an array Samples

13. Arrays Definition Declaring and populating an array Samples
var colors = new string[4];
colors[0] = “Red”;
colors[1] = “White”;
colors[2] = “Green”;
colors[3] = “Blue”;
An array is a reference type.
In this case we should use: “new” keyword for initialization.

14. Arrays Best practices Do Avoid
Use arrays when the size is known at the design time
Do not use arrays when the data comes from a database call
For an array name use ‘pluralization’ => Colors

15. Arrays Demo Working with arrays
Note: How to create a R# template for tests

16. Generic List

17. Generic List Definition Arrays vs Generic List
Declaring and populating Generic Lists
Using initializers
Retrieving elements from Generic lists
Iterating through a Generic List
Demo

18. Generic List Definition
It is a strongly typed list of elements that is accessed using a positional index number.

19. Generic List
Arrays vs Generic List

20. Generic List
Arrays vs Generic List
Arrays
Generic List

21. Generic List
Arrays vs Generic List
Arrays
Generic List
Strongly typed

22. Generic List Arrays vs Generic List Arrays Generic List Strongly typed
Fixed length
Expandable

23. Generic List Arrays vs Generic List Arrays Generic List Strongly typed
Fixed length
Expandable
The is no ability to add/remove elements
Can add, insert or remove elements

24. Generic List Arrays vs Generic List Arrays Generic List Strongly typed
Fixed length
Expandable
The is no ability to add/remove elements
Can add, insert or remove elements
Multi-dimensional
One-dimensional

25. Generic List
Declaring and populating Generic Lists

26. Generic List Declaring and populating Generic Lists
var cities = new List<string>();
cities.Add(" London");
cities.Add(" Paris");
cities.Add(" Milan");

27. Generic List Declaring and populating Generic Lists
var cities = new List<string>{“London”, “Paris”, “Milan”};
This is using Collection initializer.

28. Generic List Frequently asked questions
When is appropriate to use a generic list?

29. Generic List Frequently asked questions
When is appropriate to use a generic list?
Any time the application needs to manage a list of things
What are the key differences between an array and a generic list?

30. Generic List Frequently asked questions
When is appropriate to use a generic list?
Any time the application needs to manage a list of things
What are the key differences between an array and a generic list?
An array is fixed length and can have multiple dimensions
A generic list can have any length and provides methods to add, insert or remove elements
Execution time

31. Generic List Frequently asked questions
When is appropriate to use a generic list?
Any time the application needs to manage a list of things
What are the key difference between an array and a generic list?
An array is fixed length and can have multiple dimensions
A generic list can have any length and provides methods to add, insert or remove elements
Execution time
For this samples I used:
List<int> list = new List<int>( );
The second number is a checksum to verify they all did the same work.
static class Program {
static void Main()
Random rand = new Random(12345);
for (int i = 0; i < ; i++)
list.Add(rand.Next(5000)); }
int[] arr = list.ToArray();
int chk = 0;
Stopwatch watch = Stopwatch.StartNew();
for (int rpt = 0; rpt < 100; rpt++)
int len = list.Count;
for (int i = 0; i < len; i++)
chk += list[i];
watch.Stop();
Console.WriteLine("List/for: {0}ms ({1})", watch.ElapsedMilliseconds, chk);
chk = 0;
watch = Stopwatch.StartNew();
for (int i = 0; i < arr.Length; i++)
chk += arr[i];
Console.WriteLine("Array/for: {0}ms ({1})", watch.ElapsedMilliseconds, chk);
foreach (int i in list)
chk += i;
Console.WriteLine("List/foreach: {0}ms ({1})", watch.ElapsedMilliseconds, chk);
foreach (int i in arr)
Console.WriteLine("Array/foreach: {0}ms ({1})", watch.ElapsedMilliseconds, chk);
Console.ReadLine();
List/for: 1971ms ( ) Array/for: 1864ms ( ) List/foreach: 3054ms ( ) Array/foreach: 1860ms ( )

32. Generic List
Demo
Initialization, Add, Insert, Remove, RemoveAt;

33. What’s next …
Generic dictionaries
Generic collection interfaces
LINQ

34. Interview questions Abstract classes vs Interfaces Boxing/Unboxing
Immutable string

35. One more thing…
 "Walking on water and developing software from a specification are easy…"

36. One more thing…
  "Walking on water and developing software from a specification are easy if both are frozen."
- Edward V Berard

37. Questions
Do you have any other questions?

38. Thanks! See you next time! 