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
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
• 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
One-Dimensional Arrays
• One-dimensional array:
– 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
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
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
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
How to use a one-dimensional array’s Length property
How to use a one-dimensional array’s GetUpperBound method
Traversing a One-Dimensional Array
• Traverse an array: look at each array element,
The For Each…Next Statement
• 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
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
Two-Dimensional Arrays
• Two-dimensional array:
– Resembles a table with rows and columns
• Each element is identified by a unique combination of two subscripts: (row, column)
• Subscripts are zero-relative
Two-Dimensional Arrays (cont'd.)
• Two-dimensional array:
– 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
Two-Dimensional Arrays (cont'd.)
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
Calculate button’s Click event procedure
Dynamic Arrays
• You can re-dimension an array at run-time
• Rules for resizing arrays:
– Use can empty dimension list: Dim intArray() as Integer – Use ReDim to assign dimensions:
ReDim intArray (1 to intN, 1 to 2)
– Use ReDim to change Bounds
ReDim intArray (1 to (intN + 10), 1 to 3)
– Use Preserve keyword to save data in array
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
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
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
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