Microsoft Visual Basic 2010: Reloaded Fourth Edition Chapter Nine Arrays

Objectives After studying this chapter, you should be able to: Declare and initialize a one-dimensional array Store data in a one-dimensional array Determine the number of array elements and the highest subscript Traverse a one-dimensional array Code a loop using the For Each…Next statement Compute the total and average of a one-dimensional array’s contents Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Objectives (cont'd.) Find the highest value in a one-dimensional array Associate a list box with a one-dimensional array Use a one-dimensional array as an accumulator Sort a one-dimensional array Create and initialize a two-dimensional array Store data in a two-dimensional array Sum the values in a two-dimensional array Search a two-dimensional array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Arrays Simple variable (or scalar variable): a variable that is unrelated to any other variable in memory Array: A group of variables with the same name and data type that are related in some way Used to temporarily store related data in memory Increases the efficiency of a program Commonly used arrays: One-dimensional Two-dimensional Microsoft Visual Basic 2010: Reloaded, Fourth Edition

One-Dimensional Arrays Can be viewed as a column of variables Each variable in the array has the same name and data type Subscript: A unique number that identifies each variable in a one-dimensional array Starts at 0 for first element in the array Use array name and subscript to refer to each individual variable in the array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-1: Illustration of the naming convention for the one-dimensional sales array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

One-Dimensional Arrays (cont'd.) Element: an individual variable in the array When an array is declared: Must specify the data type, name, and highest subscript to be used First element has a subscript of 0 The array will contain one element more than the highest subscript because subscripts start at 0 Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-2: How to declare a one-dimensional array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

One-Dimensional Arrays (cont'd.) Each element in the array is initialized if no values are provided String array elements are initialized to the keyword Nothing Numeric array elements are initialized to 0 Boolean array elements are initialized to False Date array elements are initialized to 12:00 AM January 1, 0001 Microsoft Visual Basic 2010: Reloaded, Fourth Edition

One-Dimensional Arrays (cont'd.) Initial values can be specified for array elements Populating the array: assigning initial values to an array List the values in a comma-separated list enclosed in curly braces ({}) After declaration, can use an assignment statement to store a value in an array element Length property: indicates number of elements GetUpperBound method: returns the highest subscript Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-3: How to store data in a one-dimensional array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

One-Dimensional Arrays (cont'd.) Figure 9-4: How to use a one-dimensional array’s Length property Microsoft Visual Basic 2010: Reloaded, Fourth Edition

One-Dimensional Arrays (cont'd.) Figure 9-5: How to use a one-dimensional array’s GetUpperBound method Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Traversing a One-Dimensional Array Traverse an array: look at each array element, one by one, from beginning to end of the array Use a loop to traverse an array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-6: How to traverse a one-dimensional array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

The For Each…Next Statement Used to code a loop that processes each element in a group or array Creates a variable used to represent each element in the group or array Data type of the element must match the data type of the group Microsoft Visual Basic 2010: Reloaded, Fourth Edition

The For Each…Next Statement (cont'd.) Figure 9-7: How to use the For Each…Next statement Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Starward Coffee – Calculating a Total and an Average Figure 9-9: Problem specification for the Starward Coffee Application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Starward Coffee – Calculating a Total and an Average (cont’d.) Figure 9-8: Sample run of the Starward Coffee application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Starward Coffee – Calculating a Total and an Average (cont’d.) Figure 9-10: Partial code for the Starward Coffee application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-10: Partial code for the Starward Coffee application (cont’d Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Starward Coffee – Calculating a Total and an Average (cont’d.) Figure 9-10: Partial code for the Starward Coffee application (cont’d.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Car-Mart – Finding the Highest Value Figure 9-11: Problem specification for the Car-Mart application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Car-Mart – Finding the Highest Value (cont’d.) Figure 9-12: Sample run of the Car-Mart application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-13: Get Highest button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Hunt Auditorium – Arrays and Collections Figure 9-14: Problem specification for the Hunt Auditorium application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Hunt Auditorium – Arrays and Collections (cont'd.) Figure 9-15: Sample run of the Hunt Auditorium application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Hunt Auditorium – Arrays and Collections (cont'd.) Figure 9-16: Partial code and an illustration for the Hunt Auditorium application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Hunt Auditorium – Arrays and Collections (cont'd.) Figure 9-15: Partial code and an illustration for the Hunt Auditorium application (cont’d.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Hinsbrook School – Accumulator Array Figure 9-17: Problem specification for the Hinsbrook School application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Hinsbrook School – Accumulator Array (cont'd.) Figure 9-18: Sample run of the Hinsbrook School application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Hinsbrook School – Accumulator Array (cont'd.) Figure 9-19: Partial code for the Hinsbrook School application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-19: Partial code for the Hinsbrook School application (cont’d Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Sorting a One-Dimensional Array Sorting: arranging data in a specific order Ascending: first element is smallest, last element is largest Descending: first element is largest, last element is smallest Array.Sort method: used to sort elements in a one-dimensional array in ascending order Array.Reverse method: used after Array.Sort method to change to descending order Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-20: How to use the Array.Sort and Array.Reverse methods Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Two-Dimensional Arrays Resembles a table with rows and columns Each element is identified by a unique combination of two subscripts: (row, column) Subscripts are zero-relative Refer to an element using the name followed by the (row, column) pair in parentheses Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-21: Names of some of the variables contained in the two-dimensional orders array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Two-Dimensional Arrays (cont'd.) Declared with highest row subscript and highest column subscript (zero-relative) Number of rows = highest row subscript + 1 Number of columns = highest column subscript + 1 Can specify initial values for array elements If no initial values are declared, array elements are automatically initialized Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-22: How to declare a two-dimensional array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Two-Dimensional Arrays (cont'd.) Figure 9-23: How to store data in a two-dimensional array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-23: How to store data in a two-dimensional array (cont’d.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-24: How to use a two-dimensional array’s GetUpperBound method Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Traversing a Two-Dimensional Array To traverse a two-dimensional array, use two loops: Outer loop: tracks the row subscript Nested loop: tracks the column subscript Can also use a For Each…Next loop Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Traversing a Two-Dimensional Array (cont'd.) Figure 9-25: How to traverse a two-dimensional array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-25: How to traverse a two-dimensional array (cont’d.) Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Jenko Booksellers – Calculating a Total Figure 9-26: Problem specification for the Jenko Booksellers application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Jenko Booksellers – Calculating a Total (cont’d.) Figure 9-27: Sample run of the Jenko Booksellers application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Jenko Booksellers – Calculating a Total (cont’d.) Figure 9-28: Calculate button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition

O’Reilly Studios – Searching a Two-Dimensional Array Figure 9-29: Problem specification for the O’Reilly Studios application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

O’Reilly Studios – Searching a Two-Dimensional Array (cont’d.) Figure 9-30: Sample run of the O’Reilly Studios application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 9-31: Partial code for the O’Reilly Studios application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Programming Tutorial 1 Lottery Game application Generates and displays six unique random numbers for a Lottery Game Figure 9-33: MainForm in the Lottery Game application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Programming Tutorial 2 Stay Fit Health Club application Displays monthly fees for three different membership levels Figure 9-33: MainForm for the Stay Fit Health Club application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Programming Example Professor Coleman application Allows a user to select a letter grade from a list box Figure 9-43: MainForm in the Professor Coleman application Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Summary Arrays: used to store related data in memory All variables in an array have the same name and data type To declare a one-dimensional array, provide the highest subscript or initial values One-dimensional array: each element is uniquely identified by its position (subscript) in the array Refer to an element in a one-dimensional array by using array name and element’s subscript Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Summary (cont'd.) Length property: returns the number of elements in an array GetUpperBound method: returns the highest subscript in the array Use a loop to traverse a one-dimensional array Can use variables in an array as accumulators Array.Sort method: sorts the elements in a one-dimensional array in ascending order Array.Reverse method: reverses the order of elements in a one-dimensional array Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Summary (cont'd.) Two-dimensional array: each element is uniquely identified by its position (row and column subscripts) in the array To declare a two-dimensional array, provide the highest row and column subscripts or initial values Number of rows in a two-dimensional array is the highest row subscript value + 1 Number of columns in a two-dimensional array is the highest column subscript value + 1 Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Summary (cont'd.) Refer to an element in a two-dimensional array by using array name and element’s row and column subscripts separated by a comma Use a two-dimensional array’s GetUpperBound method to determine the highest row subscript and the highest column subscript in the array Can traverse a two-dimensional array using either two loops (outer loop and nested loop) or the For Each…Next statement Microsoft Visual Basic 2010: Reloaded, Fourth Edition