Chapter 7 – Arrays

1. Chapter 7 – Arrays 7.1 Creating and Accessing Arrays 7.2 Using LINQ with Arrays 7.3 Arrays of Structures 7.4 Two-Dimensional Arrays 7.5 A Case Study: Analyze a Loan

2. 7.4 Two-Dimensional Arrays • Declaring a Two-Dimensional Array Variable • Implicit Array Sizing and Initialization • The ReDim Statement • Filling a Two-Dimensional Array with a Text File • Outputting an Array

3. Declaring a Two-Dimensional Array Variable • Two-dimensional arrays store a table of items of the same type. • Consider the rows of the table as numbered 0, 1, 2, … m and the columns numbered 0, 1, 2, … n. • The array is declared with DimarrayName(m, n) AsDataType • The item in ith row, jth column is denoted arrayName(i,j)

4. Declaring a Two-Dimensional Arrays An unsized two-dimensional array can be declared with a statement of the form DimarrayName(,) As varType

5. ReDim and Two-Dimensional Arrays • An already-created array can be resized with ReDimarrayName(r, c) • which loses the current contents. • When Preserve is used … ReDim PreservearrayName(r, c) • Only the columns can be resized. • ReDim cannot change the number of rows in the array.

6. Implicit Array Sizing and Initialization Arrays can be initialized when they are declared. DimarrayName(,) As DataType= {{ROW0},{ROW1}, {ROW2}, ..., {ROWN}} declares a two-dimensional array where ROW0 consists of the entries in the top row of the corresponding table delimited by commas, and so on.

7. The row and column headers are not a part of the matrix Road-Mileage Table Dim rm(3, 3) As Double rm(0,0)=0, rm(0,1)=2054, rm(1,2)=2786

8. Implicit Array AssignmentRoad-Mileage Dimrm(,) As Double = {{0, 2054, 802, 738}, {2054, 0, 2786, 2706}, {802, 2786, 0, 100}, {738, 2706, 100, 0}} declares and initializes an array of road-mileages.

9. GetUpperBound Method After execution of the statement DimarrayName(r, c) As varType • the value of arrayName.GetUpperBound(0) is r, • and the value of arrayName.GetUpperBound(1) is c.

10. Filling a Two-Dimensional Array with a Text File Text File Distances.txt 0,2054,802,738 2054,0,2786,2706 802,2786,0,100 738,2706,100,0 In the next set of code we will read the values of this text file into a two dimensional array.

11. Filling a Two-Dimensional Array with a Text File (cont.) Dimrm(3, 3) As Double 'road mileage DimrowOfNums() AsString= IO.File.ReadAllLines("Distances.txt") Dimline, data() As String ForiAs Integer = 0To 3 line = rowOfNums(i) data = line.Split(""c) For jAs Integer= 0 To3 rm(i, j) = CDbl(data(j)) Next Next

12. Outputting Data from a Matrix Private Sub PrintMatrix(rm() as Double) ‘Print a 3 x 3 matrix Dim build as String Forrow As Integer = 0 Torm.getupperbound(0) build = “” Forcol As Integer = 0 Torm.getupperbound(1) build = build &Cstr(rm(row, col)) & “ “ Next lstbox.items.add(build) Next End Sub

13. Printing a Matrix in Zones 'Print a 3 x 3 matrix Dim rm(,) AsDouble = {{2, 3, 5}, {1, 4, 6}, {0, 7, 9}} Dim frtstr AsString = "{0,-15} {1,-15} {2,-15}" For row AsInteger = 0 To 2 ListBox1.Items.Add(String.Format(frtstr, rm(row, 0), rm(row, 1), rm(row, 2))) Next

14. Outputting To A DataGridView First create the columns for your matrix

15. Code For Outputting to a DataGridView Dim example(,) AsInteger = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}} For r AsInteger = 0 To 2 DataGridView1.Rows.Add() For c AsInteger = 0 To 3 DataGridView1.Item(c, r).Value = example(r, c) Next Next Matrices rows first, columns second DataGridView columns are listed first …Blah

16. DataGridView Column Headers Dim example(,) AsInteger = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}} For c AsInteger = 0 To 3 DataGridView1.Columns.Add(CStr(c), "Column " & c) Next For r AsInteger = 0 To 2 DataGridView1.Rows.Add() For c AsInteger = 0 To 3 DataGridView1.Item(c, r).Value = example(r, c) Next Next Column name

17. DataGridView Row Headers Dim columns() AsString = {"Column1", "Column2", "Column3"} Dim Rows() AsString = {"Row1", "Row2", "Row3"} Dim array2d(,) AsInteger = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}} For c AsInteger = 0 To columns.Count - 1 DataGridView1.Columns.Add(columns(c), columns(c)) Next For r AsInteger = 0 To Rows.Count - 1 DataGridView1.Rows.Add() DataGridView1.Rows(r).HeaderCell.Value = Rows(r) For c AsInteger = 0 To columns.Count - 1 DataGridView1.Item(c, r).Value = array2d(r, c) Next Next 1st Add the row 2nd Assign the row array to the dgv

18. Processing Each Element Using a For Each Dim nums(,) AsDouble = {{7, 3, 1, 0}, {2, 5, 9, 8}, {0, 6, 4, 10}} 'use a For Each loop Dim total AsDouble = 0 ForEach num AsDoubleIn nums If num Mod 2 = 0 Then total += num EndIf Next lstOutput.Items.Add(total) Finding the sum of the even numbers in a Matrix.

19. Processing a Matrix Using a LINQ Query Dimnums(,) AsDouble = {{7, 3, 1, 0}, {2, 5, 9, 8}, {0, 6, 4, 10}} 'use a For Each loop 'use LINQ Dim query = FromnumInnums.Cast(OfDouble)() Where (numMod 2 = 0) Selectnum lstOutput.Items.Add(query.Sum)

20. How do we add up the values in a column? Can you create a For Loop to add up the columns? 2 3 6 8 7 1 4 5 0 2 -2 9 x(0,0) x(0,1) x(0,2) x(0,3) x(0,4) x(1,0) x(1,1) x(1,2) x(1,3) x(1,4) x(2,0) x(2,1) x(2,2) x(2,3) x(2,4)