1. CSCI 3328 Object Oriented Programming in C# Chapter 7: Arrays
UTPA – Fall 2012
This set of slides is revised from lecture slides of Prof. John Abraham. -- Xiang Lian

2. Objectives In this chapter, you will:
Learn how arrays are used to store elements
Get familiar with the declaration, initialization, and reference to elements of the array
Know how to pass arrays to methods
Learn how to use multidimensional arrays
Learn how to use foreach statement to iterate through elements in the array

3. Arrays
An array is a group of variables (called elements) containing values that all have the same data type
For most languages, the number of elements are static and defined at declaration
Single dim, two dim and multiple dim

4. Example of an Array The first element is the zeroth element
C[0]
-45
C[1] 6
C[2]
C[3] 72
C[4] 34
C[5] 39
C[6] 98
C[7]
-1345
C[8]
939
C[9] 10
C[10] 40
C[11] 33
The first element is the zeroth element
The highest position number is array’s upper bound
Array C on RHS: 11
Access array elements
Use index (or subscript)
E.g., C[8]

5. Arrays (cont'd)
Data structure consisting of related data items of the same type
One variable name, multiple elements
Arrays are passed as reference type, not value
To access an element we use name of the array and index in square bracket

6. Declaring and Creating Arrays
Declaration
int[] array = new int[12]; (creates indices 0 to 11)
Or do it this way:
int[] array;
array = new int[12];
Or this way:
const int size = 12;
array = new int[size];
Since array is an object, we can resize the array as follows:
Array.Resize(ref array, 10);

7. Arrays of Other Data Types
string [] str = new string [100];
char [] ch = new char [ 50]; …

8. Initializing an Array // creates 5-element array
Initializing arrays while declaring
int [] arr = new int [] {10, 20, 30, 40, 50};
int [] array = {10,20,30,40,50};

9. Sum in an Array int[] array = {10,20,30,40,50};
// creates 5-element array
Finding the sum
double sum=0;
double average;
for (int counter =0; counter < array.Length; counter++)
sum = sum+array[counter];
size of the array

10. Average in an Array int[] array = {10,20,30,40,50};
// creates 5-element array
Finding the sum
double sum=0;
double average;
for (int counter =0; counter < array.Length; counter++)
sum = sum+array[counter];
average = sum/array.Length;

11. Standard Deviation Explained
In your assignment, assuming array has length n, the standard deviation s is given by:

12. foreach Statements In addition to for loops, you can also work with:
Syntax
foreach (type identifier in arrayName)
REMEMBER: YOU HAVE TO START WITH ELEMENT 0!

13. Syntax of foreach Statements
Example of computing summation of elements in an array called scores:
foreach (int score in scores) {
sum = sum + score; }

14. Passing Arrays by Value
Declaration
int[] firstArray={1, 2, 3};
int[] firstArrayCopy = firstArray;
public static void FirstDouble (int [] array) {
for (int i = 0; i<array.Length; i++)
array[i]*=2;
array = new int [] {11, 12, 13}; }
Call
FirstDouble(firstArray);

15. Passing Arrays by Reference
Declaration
int[] secondArray={1, 2, 3};
int[] secondArrayCopy = firstArray;
public static void SecondDouble (ref int [] array) {
for (int i = 0; i<array.Length; i++)
array[i]*=2;
array = new int [] {11, 12, 13}; }
Call
SecondDouble(ref secondArray);

16. Rectangular Arrays Rectangular array is a two dimensional array
Similar to a table with rows and columns
arrayName[row, column]
int [ , ] a = new int [3, 4];
Column 0
Column 1
Column 2
Column 3
a[0, 0]
a[0, 1]
a[0, 2]
a[0, 3]
a[1, 0]
a[1, 1]
a[1, 2]
a[1, 3]
a[2, 0]
a[2, 1]
a[2, 2]
a[2, 3]
Row 0
Row 1
Row 2

17. Nested Array Initializer
int [ , ] arr = {{1, 2}, {3, 4}} 1 2 3 4

18. Example of Rectangular Arrays
public int [,] hands = new int[5, 14];
for (i=1; i<=52; i++) {
hands[player, hand] = sdeck[i]; }

19. Jagged Arrays Tables that have rows of unequal columns
Somewhat like an array of arrays
Fixed students and exams not everyone taking it..
int [] [] scores = new int [students][];
scores[0] = new int [5]; // student 0 takes 5 exams
scores[1] = new int [4]; // student 1 takes 4 exams

20. Sort an Array C[0] -45 C[1] 6 C[2] C[3] 72 C[4] 34 C[5] 39 C[6] 98
C[3] 72
C[4] 34
C[5] 39
C[6] 98
C[7]
-1345
C[8]
939
C[9] 10
C[10] 40
C[11] 33
C[0]
-1345
C[1]
-45
C[2]
C[3] 6
C[4] 10
C[5] 33
C[6] 34
C[7] 39
C[8] 40
C[9] 72
C[10] 98
C[11]
939

21. Sort Method of Array You need to write your own sort methods later own
For now you can use:
Array.Sort(scores);
The identifier, scores, is the array you created

22. Search Method
Searching: to determine whether a value (called search key) is in the array
Linear search
Compare each element of the array with the search key
For either sorted or unsorted array
Efficient for small array
Binary search
For sorted array

23. Linear Search search key C[0] -45 C[1] 6 C[2] C[3] 72 C[4] 34 C[5] 39
C[3] 72
C[4] 34
C[5] 39
C[6] 98
C[7]
-1345
C[8]
939
C[9] 10
C[10] 40
C[11] 33

24. Binary Search You need to write your own binary search method later
But now you can use:
int index = Array.BinarySearch(array, value);
If index < 0, then value is not found in the array
Otherwise, index stores the index of value in the array

25. Binary Search first search key: 10 middle last C[0] -1345 C[1] -45
C[3] 6
C[4] 10
C[5] 33
C[6] 34
C[7] 39
C[8] 40
C[9] 72
C[10] 98
C[11]
939
first
search key: 10
middle
last

26. Binary Search first search key: 10 middle last C[0] -1345 C[1] -45
C[3] 6
C[4] 10
C[5] 33
C[6] 34
C[7] 39
C[8] 40
C[9] 72
C[10] 98
C[11]
939
first
search key: 10
middle
last

27. Binary Search first search key: 10 middle last C[0] -1345 C[1] -45
C[3] 6
C[4] 10
C[5] 33
C[6] 34
C[7] 39
C[8] 40
C[9] 72
C[10] 98
C[11]
939
first
search key: 10
middle
last

28. Binary Search first search key: 10 middle last C[0] -1345 C[1] -45
C[3] 6
C[4] 10
C[5] 33
C[6] 34
C[7] 39
C[8] 40
C[9] 72
C[10] 98
C[11]
939
first
search key: 10
middle
last

29. Copying an Array
You can copy one element at a time or the entire array
Array.Copy(fromArray, fromIndex, toArray, to Index, length);
Note: the following statement does not copy, but creates another reference to the array
string[] copyDeck = oDeck;