CSCI 3328 Object Oriented Programming in C# Chapter 7 : Arrays

1. CSCI 3328 Object Oriented Programming in C# Chapter 7: Arrays Xiang Lian The University of Texas Rio Grande Valley Edinburg, TX 78539 xiang.lian@utrgv.edu

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 foreachstatement 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 • 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 = newint[12]; • Or this way: • int[] array; • constintsize = 12; • array = newint[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 = newstring [100]; • char [] ch = newchar [ 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 (typeidentifierinarrayName) • 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 (refint [] 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 Row 0 Row 1 Row 2

17. Nested Array Initializer • int [ , ] arr = {{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

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

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 search key: 10 first middle last

26. Binary Search search key: 10 first middle last

27. Binary Search search key: 10 first middle last

28. Binary Search search key: 10 first 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;