1. INF230 Basics in C# Programming
AUBG, COS dept
Lecture 32
Title:
Arrays
(part 2)
Reference: Doyle, chap 8

2. Lecture Contents: Two-dimensional arrays including rectangular types
Two-dimensional arrays including jagged types
Multidimensional arrays
The ArrayList class to create dynamic lists

3. From Problem Analysis to Program Design
Chapter 8
Advanced Collections
C# Programming:
From Problem Analysis to Program Design
4th Edition

4. Lecture Contents:
Iteration based on data structures – the FOR…EACH type loops
Using LINQ with Arrays

5. Using Loops to access Arrays
Given an array:
int[] numbers = new int[] {5, 12, 5, 7, 12, 24, 244};
Write a while … loop to output all array elements

6. Using Loops to access Arrays
Given an array:
int[] numbers = new int[] {5, 12, 5, 7, 12, 24, 244};
Write a do … while loop to output all array elements

7. Using Loops to access Arrays
Given an array:
int[] numbers = new int[] {5, 12, 5, 7, 12, 24, 244};
Write a for loop to output all array elements

8. Using Loops to access Arrays
int cnt = 0;
while (cnt < numbers.Length) {
Console.Write(" " + numbers[cnt]); cnt += 1; }
Console.WriteLine("\n");
//===========================================
cnt = 0; do
Console.Write(" " + numbers[cnt]); cnt += 1; }
while (cnt < numbers.Length);
for (cnt=0; cnt < numbers.Length; cnt++)Console.Write(" " + numbers[cnt]);

9. Using Loops to access Arrays
Given an array:
int[] numbers = new int[] {5, 12, 5, 7, 12, 24, 244};
Write a for each loop to output all array elements

10. Using Loops to access Arrays
Given an array:
int[] numbers = new int[] {5, 12, 5, 7, 12, 24, 244};
foreach (int Val in numbers)
Console.Write(" " + Val);
// cnt is called a counter variable.
// Val is called a looping variable or iteration variable.

11. For Each Loops can be replaced with
for (int i=1; i<ages.Length; i++) {
if(ages[i] > max) max = ages[i]; }
can be replaced with
foreach (int age in ages)
if(age > max) max = age;

12. For Each Loops (continued)
In the for… loop, the counter variable i can have any name.
In the foreach loop, the looping variable age can have any name.
The primary difference between the two types of loops is that in a foreach loop no changes can be made in the values of elements of the array.

13. 7.2 Using LINQ with Arrays
LINQ Queries

14. What is LINQ? LINQ stands for Language INtegrated Query
A query is a request for information
LINQ provides a standardized way to retrieve information from data sources as
arrays,
text files,
XML documents and
data bases

15. LINQ Query
A LINQ query for an array is declarative code that describes what you want to retrieve from an array. A LINQ query is a variable – instance/object of a class (also data container) that has contents – sequence of data items extracted and filtered from a source

16. LINQ Query Code of the form range variable
var queryName = from var in arrayName source data
where [condition on var]
select var;
declares the variable queryName as a query and assigns to it a sequence of the values from arrayName that satisfy the stated condition.
query operators

17. LINQ Query (continued)
Phrases “from var in arrayName” “where [condition on var]” “select var” are called query clauses. Keywords from, where, select are called query operators. var is called a range variable. arrayName is called a source data.

18. LINQ Query (continued)
var queryName = from var in arrayName
where [condition on var]
select var;
The entire expression to the right of the equal sign = is called a query expression.

19. LINQ Query (continued)
Most query expressions begin with from clause and end with select clause. Each from clause identifies the data source and a range variable. A where clause is added to filter or exclude data from the result.

20. LINQ Query (continued)
The data flow explained (subject Input  LINQ  Output of further query processing) Data filtered Source sequence of values

21. LINQ Query (continued)
Example
// test LINQ
int[] nums = new int[] {5, 12, 5, 7, 12};
var numQuery = from num in nums
select num;
num – range variable
nums – data source /array/
from, select – query operators
from num in nums – query clause
select num – query clause
whole text to the right of equal sign – query expression

22. LINQ Query (continued)
Example
// test LINQ
int[] nums = new int[] {5, 12, 5, 7, 12};
var numQuery = from num in nums
select num;
How to view the output generated by numQuery?
See next slide

23. LINQ Query (continued)
Example
// test LINQ
int[] nums = new int[] {5, 12, 5, 7, 12};
var numQuery = from num in nums
select num;
How to view the output generated by numQuery?
foreach (int val in numQuery)
Console.WriteLine(val);

24. LINQ Query (continued)
Output saved in non text format as contents of numQuery.
The values in the sequence can be converted to an array /method toArray()/, displayed in a list box, or written to a text file.
var numQuery = …
int[] numArray = new int[10];
numArray = numQuery.ToArray();
foreach (int val in numArray) Console.WriteLine(val);

25. LINQ Query (continued)
Output saved in non text format as contents of numQuery.
Instead of fixing the array size in advance [10] as on the previous slide, we can count the actual number of array elements using extra loop.
var numQuery = from num in nums
select num;
int broi = 0;
foreach (int var in numQuery) {broi++;}
int[] arr = new int[broi];
arr = numQuery.ToArray();

26. LINQ Query (continued)
Other useful methods:
numQuery.Count()
numQuery.Average()
numQuery.Sum()

27. LINQ Query (continued)
The example was so simple:
primitive 1 to 1 copy source to output
The real power of LINQ happens when filtering the input gets involved.
The where contextual keyword operator

28. LINQ Query (continued)
int[] nums = new int[] {5, 12, 5, 7, 12}; var numQuery = from num in nums select num; // to be updated as shown below where num < 10

29. LINQ Query (continued)
int[] nums = new int[] {5, 12, 5, 7, 12}; var numQuery = from num in nums select num; // to be updated as shown below where num > 10 && num < 15

30. LINQ Query (continued)
// test LINQ The where operators are said to filter data. The select operators are said to project data.

31. LINQ Query (continued)
The variable in the Select clause can be replaced by an expression involving the variable var numQuery = from num in nums where num < 10 select num + 5 * num; Remark: Missing Select clause produces the same effect as the clause Select num.

32. Function Procedures in Queries
Methods are commonly used in Where and Select clauses
var presQuery = from pres in presidents
where FirstName(pres) =
txtFirstName.Text
select IncludeTitle(pres);
foreach (pres in presQuery)
lstPres.Items.Add(pres);

33. Function Procedures in Queries
Methods are commonly used in Where and Select clauses
var presQuery = from pres in presidents
where FirstName(pres) =
txtFirstName.Text
select IncludeTitle(pres);
OR:
lstPres.DataSource = presQuery.ToList; //???

34. Continuation of Program
String IncludeTitle(String pres) {
return "President " + pres; }

35. Order By Operator
Sorts string values into alphabetical order (either ascending or descending)
Sorts numbers into numeric order (either ascending or descending)
int[] nums = new int[] { 5, 12, 5, 7, 12 };
var numQuery = from num in nums
orderby num ascending
select num;

36. Exercises
Write a program that uses a LINQ query to calculate the sum of the numbers in the array declared below:
int[] pp = new int[10]
{ 2, 5, -5, 8, -8, 30, 50, , -80};

37. Exercises
Write a program that uses a LINQ query to calculate the average of the numbers in the array declared below:
int[] pp = new int[10]
{ 2, 5, -5, 8, -8, 30, 50, , -80};

38. Thank You
For
Your Attention!

39. Two-Dimensional Arrays
Two-dimensional and other multidimensional arrays follow same guidelines as one-dimensional
Referenced much like you reference a matrix
Two kinds of two-dimensional arrays
Rectangular
Visualized as a table divided into rows and columns
Jagged or ragged
Visualized as a table whose rows are with variable number of elements
C# Programming: From Problem Analysis to Program Design

40. Two-Dimensional Arrays (continued)
int [ , ] calories = { {900, 750, 1020}, {300, 1000, 2700},
{500, 700, 2100}, {400, 900, 1780},
{600, 1200, 1100}, {575, 1150, 1900},
{600, 1020, 1700} };
Notice how each row is grouped using curly braces. A comma is used to separate rows
Values are stored side by side in contiguous memory locations using a row major format
C# Programming: From Problem Analysis to Program Design

41. Two-Dimensional Representation
Figure 8-1 Two-dimensional structure
C# Programming: From Problem Analysis to Program Design

42. Two-Dimensional Arrays (continued)
Declaration format
type [ , ] identifier = new type [integral value, integral value];
Two integral values are required for a two-dimensional array
Number of rows listed first
Data values placed in array must be of the same base type
Example (create a 7x3 matrix)
int [ , ] calories = new int[7, 3];
C# Programming: From Problem Analysis to Program Design

43. Two-Dimensional Arrays (continued)
calories references address of calories[0,0]
Figure 8-2 Two-dimensional calories array
C# Programming: From Problem Analysis to Program Design

44. Two-Dimensional Arrays (continued)
Length property gets total number of elements in all dimensions
Console.WriteLine(calories.Length); // Returns 21
GetLength( ) – returns the number of rows or columns
GetLength(0) returns number of rows
GetLength(1) returns number of columns
Console.WriteLine(calories.GetLength(1)); //Display 3 (columns)
Console.WriteLine(calories.GetLength(0)); //Display 7 (rows)
Console.WriteLine(calories.Rank); // returns 2 (dimensions)
C# Programming: From Problem Analysis to Program Design

45. Two-Dimensional Arrays (continued)
int [ , ] calories = new int[7, 3]; Console.WriteLine(calories.GetUpperBound(0)); // Returns 6 (row index) foreach (int cal in calories) // Displays all values Console.Write(cal + " "); for (int r = 0; r < calories.GetLength(0); r++) for (int c = 0; c < calories.GetLength(1); c++) calories[r, c] = 0; // Initializes all cells
C# Programming: From Problem Analysis to Program Design

46. Two-Dimensional Arrays (continued)
Example illustrate:
Passing 2-D array as a parameter to a method
Method returning 1-D array
C# Programming: From Problem Analysis to Program Design

47. Two-Dimensional Arrays (continued Average by day - size 7)
public static double[ ] CalculateAverageByDay (int[ , ] calories) {
int sum = 0;
double[ ] dailyAverage = new double[7];
for (int r = 0; r < calories.GetLength(0); r++)
for (int c = 0; c < calories.GetLength(1); c++)
sum += calories[r, c];
dailyAverage[r] = (double)sum / calories.GetLength(1);
sum = 0; }
return dailyAverage;
Method returns array of averages…row averages
C# Programming: From Problem Analysis to Program Design

48. Two-Dimensional Arrays (continued Average by meal - size 3)
public static double[ ] CalculateAverageByMeal(int[ , ] calories) {
int sum = 0;
double[ ] mealAverage = new double[3];
for (int c = 0; c < calories.GetLength(1); c++)
for (int r = 0; r < calories.GetLength(0); r++)
sum += calories[r, c];
mealAverage[c] = (double)sum / calories.GetLength(0);
sum = 0; }
return mealAverage;
Method returns array of averages…col averages
C# Programming: From Problem Analysis to Program Design

49. Two-Dimensional Arrays (continued average Calories per Meal – void or int as return value)
public static void DisplayAverageCaloriesPerMeal (int[ , ] calories) {
double sum = 0;
for (int da = 0; da < calories.GetLength(0); da++)
for (int ml = 0; ml < calories.GetLength(1); ml++)
sum += calories[da, ml];
Console.WriteLine("\nCaloric Average Per Meal: {0:N0}",
sum / calories.Length); }
da and ml used as row/col identifiers →more representative of the data
C# Programming: From Problem Analysis to Program Design

50. Two-Dimensional Arrays (continued average Calories per Meal – void or int as return value)
public static int DisplayAverageCaloriesPerMeal (int[ , ] calories) {
double sum = 0;
for (int da = 0; da < calories.GetLength(0); da++)
for (int ml = 0; ml < calories.GetLength(1); ml++)
sum += calories[da, ml];
return sum / calories.Length; }
da and ml used as row/col identifiers →more representative of the data
C# Programming: From Problem Analysis to Program Design

51. Two-Dimensional Arrays (continued)
Figure 8-3 Output from WeeklyCalorieCounter
C# Programming: From Problem Analysis to Program Design

52. Two-Dimensional Arrays (continued)
To align numbers for output, format specifier used
Console.WriteLine("{0,-10}: {1,6}", mealTime[c ],
mealAverage[c ].ToString("N0"));
Comma separates placeholder index from width specifier
First argument ({0,-10}) indicates that the first argument should be displayed in a width of 10
Negative value in front of the 10 indicates the value should be left justified
Second argument ({1,6}) indicates the numbers are right justified in a width of 6 character positions
C# Programming: From Problem Analysis to Program Design

53. Jagged Arrays
Rectangular arrays always have a rectangular shape, like a table; jagged arrays do not
Also called ‘arrays of arrays’
Example
int[ ] [ ] anArray = new int[4] [ ];
anArray [0] = new int[ ] {100, 200};
anArray [1] = new int[ ] {11, 22, 37};
anArray [2] = new int[ ] {16, 72, 83, 99, 106};
anArray [3] = new int[ ] {1, 2, 3, 4};
C# Programming: From Problem Analysis to Program Design

54. Multidimensional Arrays
Limited only by your imagination as far as the number of dimensions
Format for creating three-dimensional array
type [ , , ] identifier =
new type [integral value, integral value, integral value];
Example (rectangular)
int [ , , ] calories = new int [4 ,7 ,3];
(4 week; 7 days; 3 meals)
Allocates storage for 84 elements
C# Programming: From Problem Analysis to Program Design

55. Multidimensional Arrays (continued)
Figure 8-4 Three-dimensional array
Upper bounds on the indexes are 3, 6, 2
C# Programming: From Problem Analysis to Program Design

56. Multidimensional Arrays (continued)
int [ , , ] calories = new int [4, 7, 4];
// Loop to place the row total in the last column, indexed by 3
for (int wk = 0; wk < calories.GetLength(0); wk++) {
for (int da = 0; da < calories.GetLength(1); da++)
for (int ml = 0; ml < calories.GetLength(2) - 1; ml++)
calories[wk, da, 3] += calories[wk, da, ml]; }
C# Programming: From Problem Analysis to Program Design

57. Multidimensional Arrays (continued)
Index from the calories array for the day
number used as index for the string day name array
C# Programming: From Problem Analysis to Program Design

58. ArrayList Class Limitations of traditional array
Cannot change the size or length of an array after it is created
ArrayList class facilitates creating listlike structure, AND it can dynamically increase or decrease in length
Similar to vector class found in other languages
Includes large number of predefined methods
using System.Collections;
C# Programming: From Problem Analysis to Program Design

59. ArrayList Class (continued)
Table 8-1 ArrayList members
C# Programming: From Problem Analysis to Program Design

60. ArrayList Class (continued)
Table 8-1 ArrayList members (continued)
C# Programming: From Problem Analysis to Program Design

61. ArrayList Class (continued)
Table 8-1 ArrayList members (continued)
C# Programming: From Problem Analysis to Program Design

62. ArrayList Class (continued)
Any predefined or user-defined type can be used as an ArrayList object
C# also includes a List<> class
List<> class requires that objects be the same type when you place them in the structure
ArrayList allows you to mix types
C# Programming: From Problem Analysis to Program Design

63. ArrayList Class (continued)
ArrayList anArray = new ArrayList( ); // Instantiates ArrayList anArray.Add("Today is the first day of the rest of your life!"); anArray.Add("Live it to the fullest!"); anArray.Add("ok"); anArray.Add("You may not get a second chance."); anArray.RemoveAt(2); // Removes the third physical one for (int i = 0; i < ar.Count; i++) //Displays elements Console.WriteLine(ar[i] );
C# Programming: From Problem Analysis to Program Design

64. ArrayList Class (continued)
Figure 8-6 Sample run from the ArrayList example
C# Programming: From Problem Analysis to Program Design

65. ArrayList Class (continued)
using System; using System.Collections; class SBArrayList { static void Main(string[] args) ArrayList ar = new ArrayList(); ar.Add("Sofia"); ar.Add("Varna"); ar.Add("Bourgas"); for (int i = ar.Count-1; i>=0; i--) Console.Write(ar[i] + " "); ar.Remove("Varna"); Console.WriteLine(); }
C# Programming: From Problem Analysis to Program Design

66. TempAgency Application Example
Figure 8-8 Problem specification for Manatee example
C# Programming: From Problem Analysis to Program Design

67. TempAgency Application Example (continued)
Table 8-3 Instance field members for the TempAgency class
C# Programming: From Problem Analysis to Program Design

68. TempAgency Application Example (continued)
Figure 8-9 Prototype
C# Programming: From Problem Analysis to Program Design

69. TempAgency Application Example (continued)
Figure Class diagrams
C# Programming: From Problem Analysis to Program Design

70. TempAgency Application Example (continued)
Figure TempAgency
class methods behavior
C# Programming: From Problem Analysis to Program Design

71. TempAgency Application Example (continued)
Figure TempAgency application output
Review TempAgency Example
C# Programming: From Problem Analysis to Program Design

72. Practical Demo Source Code Fragments

73. Practical Tasks
// two-dimensional arrays - rect or square table - matrix
Console.WriteLine("\n\n2D arrays - matrix");
int[,] matrix1 = new int[3, 5];
for (i = 0; i < 3; i++)
for (j = 0; j < 5; j++)
matrix1[i, j] = i * 5 + j * 10; {
Console.Write(" " + matrix1[i, j]);
Console.WriteLine(); }

74. Practical Tasks
// two-dimensional arrays - rect or square table - matrix
Console.WriteLine();
for (i = 0; i < matrix1.GetLength(0); i++) {
for (j = 0; j < matrix1.GetLength(1); j++)
Console.Write(" " + matrix1[i, j]); }
// iteration based on data structures - foreach
Console.WriteLine("\n2D array and iteration based on data structures");
foreach (int idd in matrix1)
Console.Write(" " + idd);

75. Practical Tasks
// two-dimensional arrays - rect or square table - matrix
// two-dimensional arrays - list of initializers
Console.WriteLine("\n2D array and list of initializers");
int[,] matrix2 = { { 51, 52, 53, 54, 55 },
{ 61, 62, 63, 64, 65 },
{ 71, 72, 73, 74, 75 } };
for (i = 0; i < matrix2.GetLength(0); i++) {
for (j = 0; j < matrix2.GetLength(1); j++)
Console.Write(" " + matrix2[i, j]);
Console.WriteLine(); }

76. Practical Tasks The difference in declaring
2D rectangular array /matrix/
and
2D jagged /ragged/ array
// two-dimensional arrays - rect or square table - matrix
// two-dimensional arrays - list of initializers
int[,] matrix2 = { { 51, 52, 53, 54, 55 },
{ 61, 62, 63, 64, 65 },
{ 71, 72, 73, 74, 75 } };
// two-dimensional arrays - special case - jagged array no 1
int[][] matrix3 = new int[3][];
matrix3[0] = new int[] { 0, 2, 4, 6, 8, 10 };
matrix3[1] = new int[] { 1, 3, 5, 7 };
matrix3[2] = new int[] { 11, 22 };

77. Practical Tasks
// two-dimensional arrays - special case - jagged array no 1
Console.WriteLine("\n2D array - special case - jagged array");
int[][] matrix3 = new int[3][];
matrix3[0] = new int[] { 0, 2, 4, 6, 8, 10 };
matrix3[1] = new int[] { 1, 3, 5, 7 };
matrix3[2] = new int[] { 11, 22 };
// display jagged arraay
for (i = 0; i < matrix3.Length; i++) {
Console.WriteLine();
for (j = 0; j < matrix3[i].Length; j++)
Console.Write(" " + matrix3[i][j]); }

78. Practical Tasks
// two-dimensional arrays - special case - jagged array no 2
int[][] matrix4;
matrix4 = new int[3][];
matrix4[0] = new int[10];
matrix4[1] = new int[6];
matrix4[2] = new int[8];
for (i = 0; i < matrix4.Length; i++) {
Console.WriteLine();
for (j = 0; j < matrix4[i].Length; j++)
Console.Write(" " + matrix4[i][j]); }

79. Practical Tasks // associative array - special case - hashtable
Console.WriteLine("\nAssociative array - hashtable - key and value");
Hashtable ht = new Hashtable();
ht.Add("Sofia", "BG");
ht.Add("Bern", "CH");
System.Windows.Forms.MessageBox.Show((string)ht["Sofia"]);
Console.WriteLine(ht["Sofia"]);
Console.WriteLine();
Hashtable htt = new Hashtable();
htt.Add(10, "BG");
htt.Add(210, "DE");
System.Windows.Forms.MessageBox.Show((string)htt[210]);
Console.WriteLine(htt[210]);

80. Thank You
For
Your Attention!