Programming Logic and Design: Arrays
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This document discusses arrays, including: 1) Arrays allow storing a group of like data types together in memory rather than creating multiple variables. Each element has a unique subscript starting from 0. 2) Loops can be used to efficiently assign values to or process the contents of arrays. Arrays can also be partially filled with a count variable tracking elements. 3) Two-dimensional arrays are like multiple identical arrays combined, requiring two size variables when declaring and accessing elements with two nested loops.
![Copyright Š 2016 Pearson Education, Inc., Hoboken NJ
8-3
8.1 Array Basics
An array allows you to store a group of items of
the same data type together in memory
â Why? Instead of creating multiple similar
variables such as employee1, employee2,
employee3 and so onâŚ
â Itâs more efficient to create just one variable
⢠Declare String employees[50]
⢠Declare Real salesAmounts[7]
â The number in the [ ] is the size of the array](https://image.slidesharecdn.com/ch08-161017001324/85/Programming-Logic-and-Design-Arrays-3-320.jpg)
![Copyright Š 2016 Pearson Education, Inc., Hoboken NJ
8-5
8.1 Array Basics
Assigning values can be done individually using
a subscriptâŚ
Set numbers[0] = 20
Set numbers[1] = 30
Set numbers[2] = 40
Set numbers[3] = 50
Set numbers[4[ = 60
But, it is much more efficient to use a Loop to
step through the array](https://image.slidesharecdn.com/ch08-161017001324/85/Programming-Logic-and-Design-Arrays-5-320.jpg)
![Copyright Š 2016 Pearson Education, Inc., Hoboken NJ
8-7
8.1 Array Basics
Arrays can be initialized to 0 or specific values
Declare String days[7] = âSundayâ, âMondayâ, âTuesdayâ,
Wednesdayâ, âThursdayâ, âFridayâ, âSaturdayâ
Array bounds checking should be performed to
avoid use of an invalid subscript
Days[7] = âSaturdayâ is invalid because there is no 7 index
â A common error is running a loop one time more than is
necessary, exceeding the bound of the array
â Off-by-one Error](https://image.slidesharecdn.com/ch08-161017001324/85/Programming-Logic-and-Design-Arrays-7-320.jpg)
![Copyright Š 2016 Pearson Education, Inc., Hoboken NJ
Constant Integer SIZE = 100
Declare Integer values[SIZE]
Declare Integer count = 0
Declare Integer number
Declare Integer Index
Display "Enter a number, or -1 to quit."
Input number
While (number != -1 AND count < SIZE)
Set values[count] = number
Set count = count + 1
Display "Enter a number, or -1 to quit."
Input number
End While
Display "Here are the values you entered:"
For index = 0 To count - 1
Display values[index]
End For
8.1 Array Basics
8-9
Partially Filled Array
Example
Thecountvariableholdsthenumberofitemsstoredinthearray.](https://image.slidesharecdn.com/ch08-161017001324/85/Programming-Logic-and-Design-Arrays-9-320.jpg)
![Copyright Š 2016 Pearson Education, Inc., Hoboken NJ
8.1 Array Basics
8-11
Constant Integer SIZE = 5
Declare Integer numbers[SIZE] = 5, 10, 15, 20, 25
Declare Integer num
For Each num In numbers
Display num
End For
For Each Example](https://image.slidesharecdn.com/ch08-161017001324/85/Programming-Logic-and-Design-Arrays-11-320.jpg)
![Copyright Š 2016 Pearson Education, Inc., Hoboken NJ
8-12
8.2 Sequentially Searching an Array
A sequential search algorithm is a simple technique for finding an
item in a string or numeric array
â Uses a loop to sequentially step through an array
â Compares each element with the value being searched for
â Stops when the value is found or the end of the array is hit
Set found = False
Set index = 0
While found == False AND index <= SIZE -1
If (array[index] == searchValue Then
Set found = True
Else
Set index = index + 1
End If
End While](https://image.slidesharecdn.com/ch08-161017001324/85/Programming-Logic-and-Design-Arrays-12-320.jpg)
![Copyright Š 2016 Pearson Education, Inc., Hoboken NJ
8-16
8.3 Processing the Contents of an Array
Copying an array can be done using loops
For index = 0 to SIZE â 1
Set secondArray[index] = firstArray[index]
End For
Passing an Array as an Argument
â Usually must pass the array and the size
The module call
getTotal(numbers, SIZE)
The module header
Function Integer getTotal (Integer array[], Integer arraySize)](https://image.slidesharecdn.com/ch08-161017001324/85/Programming-Logic-and-Design-Arrays-16-320.jpg)
![Copyright Š 2016 Pearson Education, Inc., Hoboken NJ
8-19
8.5 Two-Dimensional Arrays
Two size variables are required when declaring
Constant Integer ROWS = 3
Constant Integer COLS = 4
Declare Integer values[ROWS][COLS]
Accessing is done with two loops, and both subscripts
For row = 0 To ROWS -1
For col = 0 To COLS â 1
Display âEnter a number.â
Input values[row][col]
End For
End For](https://image.slidesharecdn.com/ch08-161017001324/85/Programming-Logic-and-Design-Arrays-19-320.jpg)
![Copyright Š 2016 Pearson Education, Inc., Hoboken NJ
8-20
8.6 Arrays of Three or More Dimensions
Arrays can also be three or more dimensions
Declare Real seats[3][5][8]
Figure 8-22 A three-
dimensional array](https://image.slidesharecdn.com/ch08-161017001324/85/Programming-Logic-and-Design-Arrays-20-320.jpg)
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Programming Logic and Design: Arrays
- 1. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ CHAPTER8 Arrays
- 2. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-2 Chapter Topics 8.1 Array Basics 8.2 Sequentially Searching an Array 8.3 Processing the Contents of an Array 8.4 Parallel Arrays 8.5 Two-Dimensional Arrays 8.6 Arrays of Three or More Dimension
- 3. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-3 8.1 Array Basics An array allows you to store a group of items of the same data type together in memory â Why? Instead of creating multiple similar variables such as employee1, employee2, employee3 and so on⌠â Itâs more efficient to create just one variable ⢠Declare String employees[50] ⢠Declare Real salesAmounts[7] â The number in the [ ] is the size of the array
- 4. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-4 8.1 Array Basics ⢠The storage locations in an array are elements ⢠Each element of the array has a unique number called a subscript that identifies it â the subscript starts at 0 in most languages. Figure 8-1 Array subscripts
- 5. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-5 8.1 Array Basics Assigning values can be done individually using a subscript⌠Set numbers[0] = 20 Set numbers[1] = 30 Set numbers[2] = 40 Set numbers[3] = 50 Set numbers[4[ = 60 But, it is much more efficient to use a Loop to step through the array
- 6. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-6 8.1 Array Basics Figure 8-3 Contents of the hours array
- 7. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-7 8.1 Array Basics Arrays can be initialized to 0 or specific values Declare String days[7] = âSundayâ, âMondayâ, âTuesdayâ, Wednesdayâ, âThursdayâ, âFridayâ, âSaturdayâ Array bounds checking should be performed to avoid use of an invalid subscript Days[7] = âSaturdayâ is invalid because there is no 7 index â A common error is running a loop one time more than is necessary, exceeding the bound of the array â Off-by-one Error
- 8. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8.1 Array Basics ⢠Partially Filled Array â Sometimes an array is only partially filled â To avoid processing the unfilled elements, you must have an accompanying integer variable that holds the number of items stored in the array. ⢠When the array is empty, 0 is stored in this variable ⢠The variable is incremented each time an item is added to the array ⢠The variable's value is used as the array's size when stepping through the array. 8-8
- 9. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ Constant Integer SIZE = 100 Declare Integer values[SIZE] Declare Integer count = 0 Declare Integer number Declare Integer Index Display "Enter a number, or -1 to quit." Input number While (number != -1 AND count < SIZE) Set values[count] = number Set count = count + 1 Display "Enter a number, or -1 to quit." Input number End While Display "Here are the values you entered:" For index = 0 To count - 1 Display values[index] End For 8.1 Array Basics 8-9 Partially Filled Array Example Thecountvariableholdsthenumberofitemsstoredinthearray.
- 10. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8.1 Array Basics ⢠Optional Topic: The For Each Loop â Some languages provide a For Each loop â It works with an array, iterating once for each array element â During each iteration, the loop copies an element's value to a variable. 8-10
- 11. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8.1 Array Basics 8-11 Constant Integer SIZE = 5 Declare Integer numbers[SIZE] = 5, 10, 15, 20, 25 Declare Integer num For Each num In numbers Display num End For For Each Example
- 12. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-12 8.2 Sequentially Searching an Array A sequential search algorithm is a simple technique for finding an item in a string or numeric array â Uses a loop to sequentially step through an array â Compares each element with the value being searched for â Stops when the value is found or the end of the array is hit Set found = False Set index = 0 While found == False AND index <= SIZE -1 If (array[index] == searchValue Then Set found = True Else Set index = index + 1 End If End While
- 13. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-13 8.3 Processing the Contents of an Array Totaling the values in an array and calculating average â Loops are used to accumulate the values â Then, the total is simply divided by the size
- 14. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ Example 8-14
- 15. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-15 8.3 Processing the Contents of an Array Finding the highest & lowest values in an array ⢠The highest â Create a variable to hold the highest value â Assign the value at element 0 to the highest â Use a loop to step through the rest of the elements â Each iteration, a comparison is made to the highest variable â If the element is greater than the highest value, that value is then the assigned to the highest variable ⢠The lowest â Same process, but checks if the element is less than the lowest value
- 16. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-16 8.3 Processing the Contents of an Array Copying an array can be done using loops For index = 0 to SIZE â 1 Set secondArray[index] = firstArray[index] End For Passing an Array as an Argument â Usually must pass the array and the size The module call getTotal(numbers, SIZE) The module header Function Integer getTotal (Integer array[], Integer arraySize)
- 17. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-17 8.4 Parallel Arrays By using the same subscript, you can establish a relationship between data stored in two or more arrays Figure 8-14 The names and addresses arrays
- 18. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-18 8.5 Two-Dimensional Arrays A two-dimensional array is like several identical arrays put together â Suppose a teacher has six students who take five tests Figure 8-17 Two- dimensional array with six rows and five columns
- 19. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-19 8.5 Two-Dimensional Arrays Two size variables are required when declaring Constant Integer ROWS = 3 Constant Integer COLS = 4 Declare Integer values[ROWS][COLS] Accessing is done with two loops, and both subscripts For row = 0 To ROWS -1 For col = 0 To COLS â 1 Display âEnter a number.â Input values[row][col] End For End For
- 20. Copyright Š 2016 Pearson Education, Inc., Hoboken NJ 8-20 8.6 Arrays of Three or More Dimensions Arrays can also be three or more dimensions Declare Real seats[3][5][8] Figure 8-22 A three- dimensional array