Csc153 chapter 06

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Csc153 chapter 06

  1. 1. Microsoft Visual C# 2010 Fourth Edition Chapter 6 Using Arrays
  2. 2. Objectives• Declare an array and assign values to array elements• Access array elements• Search an array using a loop• Use the BinarySearch(), Sort(), and Reverse() methods• Use multidimensional arrays• Learn about array issues in GUI programsMicrosoft Visual C# 2010, Fourth Edition 2
  3. 3. Declaring an Array and Assigning Values to Array Elements• Array – List of data items that all have the same data type and the same name – Each item is distinguished from the others by an index• Declaring and creating an array double[] sales; sales = new double[20];• new operator – Used to create objects• You can change the size of an arrayMicrosoft Visual C# 2010, Fourth Edition 3
  4. 4. Declaring an Array and Assigning Values to Array Elements (contd.)• Array element – Each object in an array• Subscript (or index) – Integer contained within square brackets that indicates the position of one of an array’s elements – Array’s elements are numbered beginning with 0• “Off by one” error – Occurs when you forget that the first element in an array is element 0Microsoft Visual C# 2010, Fourth Edition 4
  5. 5. Declaring an Array and Assigning Values to Array Elements (contd.)Microsoft Visual C# 2010, Fourth Edition 5
  6. 6. Declaring an Array and Assigning Values to Array Elements (contd.)• Assigning a value to an array element sales[0] = 2100.00;• Printing an element value Console.WriteLine(sales[19]);Microsoft Visual C# 2010, Fourth Edition 6
  7. 7. Initializing an Array• In C#, arrays are objects – Arrays are instances of a class named System.Array• Initializing objects – Numeric fields: 0 – Character fields: ‘u0000’ or null – bool fields: false• Initializer list – List of values provided for an arrayMicrosoft Visual C# 2010, Fourth Edition 7
  8. 8. Initializing an Array (contd.)• Initializer list examples int[] myScores = new int[5] {100, 76, 88, 100, 90}; int[] myScores = new int[] {100, 76, 88, 100, 90}; int[] myScores = {100, 76, 88, 100, 90};Microsoft Visual C# 2010, Fourth Edition 8
  9. 9. Accessing Array Elements• The power of arrays becomes apparent when you use subscripts – Can be variables rather than constant values• Using a loop to perform arithmetic on each element for (int sub = 0; sub < 5; ++sub) myScores[sub] += 3;Microsoft Visual C# 2010, Fourth Edition 9
  10. 10. Using the Length Property• Length property – Member of the System.Array class – Automatically holds an array’s length• Examples int[] myScores = {100, 76, 88, 100, 90}; Console.WriteLine(“Array size is {0}”, myScores.Length); for (int x = 0; x < myScores.Length; ++x) Console.WriteLine(myScores[x]);Microsoft Visual C# 2010, Fourth Edition 10
  11. 11. Using foreach• foreach statement – Cycles through every array element without using a subscript – Uses a temporary iteration variable • Automatically holds each array value in turn• Example double[] payRate = {6.00, 7.35, 8.12, 12.45, 22.22}; foreach(double money in payRate) Console.WriteLine(“{0}”, money.ToString(“C”));Microsoft Visual C# 2010, Fourth Edition 11
  12. 12. Using foreach (contd.)• Used under the following circumstances – When you want to access every array element – Since the iteration variable is read-only • You cannot assign a value to itMicrosoft Visual C# 2010, Fourth Edition 12
  13. 13. Using foreach with EnumerationsMicrosoft Visual C# 2010, Fourth Edition 13
  14. 14. Searching an Array Using a Loop• Searching options – Using a for loop – Using a while loopMicrosoft Visual C# 2010, Fourth Edition 14
  15. 15. Using a for Loop to Search an Array• Use a for statement to loop through the array – Set a Boolean variable to true when a match is found• Solution is valid even with parallel arraysMicrosoft Visual C# 2010, Fourth Edition 15
  16. 16. Using a for Loop to Search an Array (contd.)Microsoft Visual C# 2010, Fourth Edition 16
  17. 17. Using a while Loop to Search an Array• Use a while loop to search for a matchMicrosoft Visual C# 2010, Fourth Edition 17
  18. 18. Microsoft Visual C# 2010, Fourth Edition 18
  19. 19. Searching an Array for a Range Match• Range match – Determines the pair of limiting values between which a value fallsMicrosoft Visual C# 2010, Fourth Edition 19
  20. 20. Searching an Array for a Range Match (contd.)Microsoft Visual C# 2010, Fourth Edition 20
  21. 21. Using the BinarySearch(), Sort(),and Reverse() Methods• System.Array class contains a variety of useful, built-in methods that can search, sort, and manipulate array elementsMicrosoft Visual C# 2010, Fourth Edition 21
  22. 22. Using the BinarySearch() Method• BinarySearch() method – Finds a requested value in a sorted array – Member of the System.Array class• Do not use BinarySearch() under these circumstances – If your array items are not arranged in ascending order – If your array holds duplicate values and you want to find all of them – If you want to find a range match rather than an exact matchMicrosoft Visual C# 2010, Fourth Edition 22
  23. 23. Using the BinarySearch() Method (contd.)Microsoft Visual C# 2010, Fourth Edition 23
  24. 24. Using the Sort() Method• Sort() method – Arranges array items in ascending order – Use it by passing the array name to Array.Sort()Microsoft Visual C# 2010, Fourth Edition 24
  25. 25. Using the Sort() Method (contd.)Microsoft Visual C# 2010, Fourth Edition 25
  26. 26. Using the Reverse() Method• Reverse() method – Reverses the order of items in an array – Element that starts in position 0 is relocated to position Length – 1 – Use it by passing the array name to the methodMicrosoft Visual C# 2010, Fourth Edition 26
  27. 27. Using the Reverse() Method (contd.)Microsoft Visual C# 2010, Fourth Edition 27
  28. 28. Using Multidimensional Arrays• One-dimensional or single-dimensional array – Picture as a column of values – Elements can be accessed using a single subscript• Multidimensional arrays – Require multiple subscripts to access the array elements – Two-dimensional arrays • Have two or more columns of values for each row • Also called rectangular array, matrix, or a tableMicrosoft Visual C# 2010, Fourth Edition 28
  29. 29. Using Multidimensional Arrays (contd.)Microsoft Visual C# 2010, Fourth Edition 29
  30. 30. Using Multidimensional Arrays (contd.)Microsoft Visual C# 2010, Fourth Edition 30
  31. 31. Using Multidimensional Arrays (contd.)Microsoft Visual C# 2010, Fourth Edition 31
  32. 32. Using Multidimensional Arrays (contd.)• Three-dimensional arrayMicrosoft Visual C# 2010, Fourth Edition 32
  33. 33. Using Multidimensional Arrays (contd.)• Jagged array – One-dimensional array in which each element is another one-dimensional array – Each row can be a different lengthMicrosoft Visual C# 2010, Fourth Edition 33
  34. 34. Using Multidimensional Arrays (contd.)Microsoft Visual C# 2010, Fourth Edition 34
  35. 35. Array Issues in GUI Programs• If array values change based on user input – Array must be stored outside any method that reacts to the user’s event Microsoft Visual C# 2010, Fourth Edition 35
  36. 36. Array Issues in GUI Programs (contd.)Microsoft Visual C# 2010, Fourth Edition 36
  37. 37. You Do It• Activities to explore – Creating and Using an Array – Using the Sort() and Reverse() Methods Microsoft Visual C# 2010, Fourth Edition 37
  38. 38. Summary• An array is a list of data items – All of which have the same type and the same name – Items are distinguished using a subscript or index• In C#, arrays are objects of a class named System.Array• The power of arrays becomes apparent when you begin to use subscripts• Subscript you use remains in the range of 0 through length -1Microsoft Visual C# 2010, Fourth Edition 38
  39. 39. Summary (contd.)• foreach statement cycles through every array element without using subscripts• You can compare a variable to a list of values in an array• You can create parallel arrays to more easily perform a range match• The BinarySearch() method finds a requested value in a sorted array• The Sort() method arranges array items in ascending orderMicrosoft Visual C# 2010, Fourth Edition 39
  40. 40. Summary (contd.)• The Reverse() method reverses the order of items in an array• Multidimensional arrays require multiple subscripts to access the array elements• Types of multidimensional arrays – Two-dimensional arrays (rectangular arrays) – Three-dimensional arrays – Jagged arraysMicrosoft Visual C# 2010, Fourth Edition 40

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