Matakuliah
Tahun
Versi
: D0524 / Algoritma dan Pemrograman Komputer
: 2005
:
Pertemuan 11
Array
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menerapkan penggunaan array dalam aplikasi
2
Outline Materi
• Introduction to Array
• Declaring an Array
• Using Arrays
3
Introduction to Array
• Up to now, we have dealt with single value data
only: e.g. -47.29, True, “Smith”
• For each data item we have used a single
variable name: e.g. sum, endOfInput, aName
• Suppose we need to store the names of
everyone in this group.
• We could use a unique name for each variable,
e.g. name1, name2, name3 …
• This would be time-consuming, tedious and
unworkable with even larger sets of numbers
4
List Structures
• We can treat this kind of data as a group of
related items, rather than separate ones
• We can reserve a storage area large enough for
all the values then assign a name to the area
• This data structure may be called a single-level
table, a list, a vector or a one-dimensional array
5
Array Subscripts
• The group (array or list) is given a name, but the
individual items in the group are referred to by
their position in the array – using a subscript in
brackets
• So with a group called students, students(3) is
the 4th value (as the numbering starts at 0).
• It is similar to a street where all the houses have
the same street name, but are distinguished by
their house number.
6
Why Use Arrays
• Being able to group data into lists or arrays is an
advantage
– mirrors the real world way of working
• much data in business and science is already grouped
– allows computer memory to be used most effectively
• efficient allocation of storage to variables
• faster data access to array elements
– allows the writing of efficient program code
• write the code to process one value in the array
• then make it repeat for all the other values
7
Common Array Processing Task
• Array initialisation
• Input of data to an array (from keyboard or
external data file)
• Output of the contents of an array (to screen or
external data file)
• Searching an array for a specific value
• Counting or summing values in the array
8
Array
• Imagine we need to store the marks of a group
of 10 students studying VB. We decide to store
the marks in an array called VBmarks.
• If we could visualise the array, it might look like
this.
VBmarks(0)
VBmarks(9)
9
Declaring an Array
• To declare an array, we need to:
– give the array an identifier
– state how many data elements the array
should hold
– specify the type of data to be held in that
array
• E.g.
– Dim vbMarks (0 To 9) as Integer
10
Initialize the Array
• It is good practice to initialise (set to a known value) variables before
use.
• So we will initialise all the array elements to zero:
FOR posisi = 0 TO 9
VBmarks(posisi) = 0
NEXT posisi
• You might now visualise the array as this:
0
0
0
0
0
0
0
0
0
0
11
Exercise 1 – Input / Output Data
• Now we might input marks from the keyboard into the array
FOR posisi = 0 TO 9
keyInput VBmarks(posisi)
NEXT posisi
55

22
68
49
81
49
35
56
55
49
and then display them on the screen
FOR posisi = 0 TO 9
conOutputput VBmarks(posisi)
NEXT posisi
12
Exercise 2 – Find Highest
Value in the List
• How can we set about finding that out?
• Our human eyes can easily pick out the highest
value but the computer cannot do that.
• It must inspect each value in turn.
• It can keep a record of the value that is ‘highest
found so far’ and compare that to the next value
• if the next value is higher, it becomes ‘highest
found so far’ otherwise, the old value is kept
• After inspecting each value, it will know the highest
value
55
22
68
49
81
49
35
56
55
49
13
Exercise 2 – Solution
tertinggi = 0
FOR posisi = 0 TO 9
IF VBmarks(posisi) > tertinggi THEN
tertinggi = VBmarks(posisi)
ENDIF
NEXT posisi
conOutput tertinggi
Exercise:
1. Amend the design so that the array position of the highest
mark is output, not the mark itself
2. Amend the design so that the lowest mark in the set is
output.
14
Exercise 3 - Calculate the
Average Mark
• We often want to know the average (mean) mark.
What is the average of this set of marks?
• Write the program design to solve this problem
55
22
68
49
81
49
35
56
55
49
15
Exercise 4: Counting array
elements
Find out the number of students who passed the
module (by gaining 40 or more marks).
To do this we have to initialise a counter and
process through the array, counting the number of
marks that are equal to or greater than 40.
Write the program design to solve this problem.
55
22
68
49
81
49
35
56
55
49
16
Exercise 5: Using two arrays
• Sometimes, information from one array is
processed and the results sent to another array
or to a data file.
• In our example, if a student passes the VB
module, by gaining 40 or more marks, then they
have earned 20 more credits to their degree
credit score.
• The students’ associated degree credit scores
are held in an array called ‘credits’ in matching
positions
• When a student passes a module, the value at
the same subscript position in ‘credits’ must be
incremented by 20
17
Exercise 5 cont’d
Develop the pseudocode solution to: set up the values
as shown in the credits array (by assignment not by
input from the keyboard), input a set of student marks
into VBmarks from the keyboard and process through
VBmarks, adding 20 to the existing value in the credits
array if the value in VBmarks at the same subscript
position is >= 40 (student has passed VB)
VBmarks
55 22 68 49 81 49 35 56 55 49
credits
40 50 40 30 30 60 70 50 40 30
18