ProgrammingSoftwareBooklet - PEGSnet

Programming and
Software Development
Year 10 Information Technology
Semester Two
Penleigh and Essendon Grammar School
Programming and Software Development
Programming is the process of writing programs and developing software. A program
is a collection of instructions that, when executed, will complete a task on the
computer. People who write programs are called programmers or software
developers. Programmers write programs using programming languages. There are
many programming languages available such as Java, Visual BASIC and C++.
Each language has its own set of rules (syntax) which must be strictly followed.
However, there are basic programming concepts in all programming languages.
1. Basic Programming Concepts
When writing a program it is necessary to consider the input, processing and output.
Input is the data needed to solve the problem, the processing is the calculations
required and the output is the way of giving the solution. A program is written in a
programming language using the following concepts.
a. Keywords
In computer programming, a keyword is a word or identifier that has a particular
meaning to the programming language. Keywords help to identify the syntax of the
language (syntax being the rules that structure the programming grammar). In most
modern editors, the keywords are automatically set to have a particular text colour
to remind or inform the programmers that they are keywords. An example of a
keyword in REALBasic is MouseDown. This word already has a special meaning in
REALBasic and cannot be used as a name of a variable, constant or object.
b. Variables
Variable is an item of data that may take different values, one at a time. They are
storage containers used to hold data of the same type. To declare a variable, you
must give it a name (identifier) and state its data type.
c. Constant
Constant is an item of data with only one specific value. Constants are either
numbers or strings (group of characters)
d. Assignment Statement
Assignment statement gives a value to a variable such as: x = 9.
The general form of an assignment statement is: variable = expression. The
expression can contain other variables such as: y + 1. This will result in the
assignment statement: x = y + 1.
e. Identifier
Identifier is the name of anything in a program such as a variable. There are some
restrictions on the use of identifiers, such as always starting with a letter.
Programmers must give meaningful names to the objects (controls) that they use for
ease of understanding code. The following naming convention must be followed.
 Adding a lowercase prefix to the name they give the control quickly identifies
the object type.
 An underscore is then entered to separate the parts of the identifier. No
spaces are permitted.
 It is the followed by the name they give the object, which should begin with a
capital letter.
For example if the purpose of an edit field (control) is for the user to type in a
person’s salary then you might name it ef_Salary. Whenever you come across this in
your code you would know it was a edit field from the ef prefix, and the ‘Salary’ part
would give a strong clue as to its purpose. Examples of prefixes in REALBasic include:
Control Type
Radio Buttons
f. Function
A function is a reserved word for a particular purpose. Some functions are very
powerful, such as IF and WHILE. Programming languages mainly have two types of
1. Those built in functions which are supplied as part of the language
2. User-defined functions which you write yourself
g. Subprograms
When programming, a program may be best solved when it is broken down into
smaller parts. Then each part is solved separately and then combined to produce the
final solution. This is called structured programming. A structured program consists
of a collection of smaller programs. Each of these smaller programs is called a
subprogram. A subprogram is a self-contained section of code that performs a
particular task. Subprograms have the added advantage of being reuseable.
Programmers may use the same subprogram many times in different problems. This
reduces the time required to program. Programmers keep a ‘library’ of subprograms
they have written.
Define the term ‘program’.
Explain the difference between:
a. a constant and variable
b. function and an identifier –
Describe an advantage of subprograms.
In Exercise 2 of the REALBasic booklet you change the colour of some text
using Push Buttons. You use the following code.
Sub Action()
st_message.textcolor = &cFF0000
End Sub
a. What Keywords are used?
b. What is the Identifier? _______________________
c. What is the Assignment Statement?
2. Data Types
Data type is the kind of data that can be stored in a variable. To create a variable it
must be declared. Variable declaration involves stating the data type of the variable
and an identifier or unique name for the variable.
The following is an example of a variable declaration in REALBasic:
Data Type
Dim vi_Age as Integer
Keywords for declaring variables
Most programming languages have the following data types:
a. Integer
Integer number is a whole number without fractional parts.
b. Real Numbers
Real numbers are also known as floating-point number, and is a number with the
fractional parts.
c. Boolean
Boolean is used to store values that have one of two possible states such as true or
d. Character
Character is used to store one character such as a letter, number or symbol.
e. String
String is used to store more than one character.
3. Data operators
Data operators (or operators) are used to represent an action to be performed such
as a calculation. Operators are classified as:
a. Arithmetic operator
Performs a calculation such as addition (+), subtraction (–), division (/), multiplication
(*), powers (^) and modulus (%). Calculations are carried out using the standard
order of operations.
b. Relational operator
Compares two values and returns a boolean (true or false) result. Relational
operators include less than (<), greater than (>), less-than-or-equal-to (<=), greaterthan-or-equal-to (>=), equal-to and not-equal-to.
c. Logical operator
Compares two values and returns a boolean (true or false) result. Logical operators
include AND, OR and NOT.
Complete the table by stating the data type for each example.
Data Type
Explain the difference between an arithmetic operator and a relational
Using REALBasic coding as in the example on page 6 of this booklet, declare
the following as variables:
a. An integer for test results.
b. If you have been selected in hockey team or not?
c. The letter grade for your semester result in your reports.
4. Algorithms
An algorithm is a series of steps designed to solve a problem in a finite time. An
algorithm can be used to solve many types of problems. Algorithms are not programs
but are an important part in the development of a program.
All algorithms have the following characteristics:
 They are finite, that is, they always have an end.
 They use precise steps.
 They are designed to describe a problem in a way that will always be
understood to mean the same thing.
Algorithms can be used to describe simple daily actions or explain a particular task.
For example:
Algorithm to make a phone call:
Pick up the phone.
Dial number.
Deliver the message.
Hang up the phone.
In this example the algorithm presents a solution in a definite number of steps. Each
step is short enough so that it can be easily carried out. The steps must also be
performed in a particular order (sequence) to solve the problem; for example, you
cannot hang up the phone before delivering the message.
Algorithms are represented in a number of different ways. These are referred to as
methods of algorithm description. There are many different methods of algorithm
description such as pseudocode and flowcharts.
a. Pseudocode
Pseudocode uses indented lines and keywords to describe an algorithm. Pseudocode
is written using a word processor and is similar to many programming languages. The
flow of control in pseudocode is always from the top to the bottom. The keywords
are highlighted in capital letters (or bold) to emphasise them and to indicate the type
of action being performed. The most common keywords are shown in Table 1.
These keywords are grouped together in pairs. For example, for every BEGIN there is
an END, for every IF there is an ENDIF. Indentation is used to show the structure of
the algorithm.
The rules for using pseudocode include:
Keywords are written in capitals.
Basic keywords come in pairs, for example, for every BEGIN there is an
END, for every IF there is an ENDIF.
Indenting is used to show the structure in the algorithm.
The names of subprograms are underlined
Table 1: Keywords used in Pseudocode
Problem: Write pseudocode to calculate the area of a rectangle given a length of 3
cm and a width of 5 cm.
Make length 3 cm
Make width 5 cm
Set area to length × width
Display area
b. Flowcharts
Flowcharts are a pictorial method of describing algorithms using a set of symbols,
connecting lines and arrows.
The rules for flowcharts are:
 There is only ever one way into a flowchart structure and one way out.
 A single flowchart should fit on one page. If the flowchart doesn’t fit on one page,
then subprograms should be used.
 The main direction of flow is from top to bottom or left to right. Lines and arrows
called flowlines indicate this flow of control.
 Flowlines do not need an arrow if the flow of control is following these main
Table 2: Symbols and their meanings for a flowchart
Problem: Write pseudocode to calculate the area of a rectangle given a length of 3
cm and a breadth of 5 cm.
1. Write answers to the following questions.
a. What is an algorithm?
b. How is pseudocode different from flowcharts?
c. Why must the steps in an algorithm be performed in a particular
d. Why are the keywords in pseudocode highlighted?
e. What is the purpose of indentation in pseudocode?
f. What are the disadvantages of a flowchart?
2. True or false? Indicate with a T or an F in the far column.
a. Algorithms are a never-ending series of
steps to solve a problem.
b. The steps to solving a problem can be
carried out in any order.
c. Algorithms are only written to solve
computer problems.
d. ‘Good’ algorithms are produced when
the problem to be solved is thoroughly
e. There is only one correct solution to
every problem.
f. Once a problem is solved there is no
need to modify the solution.
3. The following algorithms have errors in their sequence. Find these errors and
number the steps to correctly solve the problem.
a. Algorithm to read a book:
Read book
Open book to first page
Close book
Get book
b. Algorithm to run a bath:
If bath is full, turn off the taps
If water is too hot, increase the
amount of cold water
Put plug into bath
If water is too cold, increase the
amount of hot water
Turn on the hot water tap
Turn on the cold water tap
5. Control Structures
Programmers solve a problem by designing an algorithm and then coding the
algorithm into a programming language. Algorithms and programming languages
consist of control structures. Control structures are the building blocks of the
program. There are three basic control structures: sequence, selection and
a. Sequencing
b. Selection
c. Repetition
a. Sequencing
Sequencing is the most common form of control structure. Each step of the
algorithm is carried out in order of its position. Each step is done only once.
Analyse the example on the table below to understand the rules about how to write
sequences in both pseudocode and algorithms.
Table 3: SEQUENCING - Design an algorithm to wash you hands.
Pseudocode Solution
Algorithm Solution
Wet hands
Clean hands with soap
Rinse off soap
Dry hands
In pseudocode, the steps are placed
between BEGIN and END (see the table
below). The sequence of four steps is
indented to show structure and to
improve the readability of the algorithm.
The flow of control is top to bottom,
starting at the first step and finishing at
the last step.
Flowcharts always start and finish with a
terminal symbol (oval). The steps are
placed between these symbols and
joined by flowlines. The direction of flow
is down the page between the terminal
Write answers to the following questions.
1. A pseudocode algorithm is provided which will allow the user to input two
whole numbers and output the sum of the two numbers.
Get 2 numbers
Store in num1 and num2
Calculate sum (num1 + num2)
Output sum
Write the flow chart algorithm to solve the same problem.
2. The flow chart shows a sequence of steps involving in buttering and eating a
slice of bread. Write the pseudocode algorithm to solve the same problem.
Flowchart Answer:
Pseudocode Answer:
b. Selection
Selection is used to make a logical decision. It requires a choice to be made between
two or more options. The choice is made depending on the answer to a condition.
There are two types of selection: binary and case. For the purposes of this course, we
will only examine binary selection.
Binary selection involves two choices
Analyse the example on the table below to understand the rules about how to write
binary selection in both pseudocode and algorithms.
Table 4: BINARY SELECTION – Design an algorithm for turning on the lights.
Pseudocode Solution
Algorithm Solution
IF night
THEN turn lights on
ELSE turn lights off
In pseudocode the keywords
IF ... THEN ... ELSE are used
for binary selection. The
condition is put after the IF
keyword. There are only two
possible answers to the
condition, true or false. If the
condition is true then the
process after the THEN
keyword is executed. If the
condition is false then the
process after the ELSE
keyword is executed. The
ELSE statement is not always
required and can be omitted.
In a flowchart the selection is made using a decision
symbol (diamond). The condition is placed inside this
symbol and the answer must be true or false. It is very
important that the two flowlines from the decision
symbol are labelled with true or false to determine
which path to follow. The two flowlines join together to
complete the binary selection.
1. Complete these algorithms using binary selection.
a. A set for instructions to follow when driving towards a set of traffic
control lights. Pseudocode algorithm:
IF lights are green
THEN drive through intersection
ELSE ____________
b. Flowchart algorithm for the same problem.
c. Repetition
A repetition is also known as an iteration or loop. It allows a number of steps to be
repeated until some condition is satisfied. The steps to be repeated are referred to
as the body of the loop. It is very important that each loop contains a condition to
stop the loop going on forever. There are two types of repetition: pre-test or posttest.
In pre-test loops the condition is tested at the start of the loop. If the condition is
false the first time, the processes will NEVER be carried out. Pre-test loops end when
the condition is false. Pre-test loops are also known as guarded loops because the
loop is only operated when the condition is met.
Analyse the example on the table below to understand the rules about how to write
pre-test loops in both pseudocode and algorithms.
Table 5: PRE TEST LOOP - an algorithm for how to use a seat belt in a car
Pseudocode Solution
Algorithm Solution
WHILE car is moving keep
seat belts on
In a pre-test repetition or
guarded loop the condition is
checked at the beginning of
the loop before the steps to
be repeated are executed. In
pseudocode the keywords
used for a pre-test repetition
condition is put after the
WHILE keyword and the
body of the loop between
In a flowchart the pre-test repetition is made using a
decision symbol and flowlines. The condition is placed
inside the decision symbol and checked before the
body of the loop.
In post-test loops the condition is tested at the end of the loop. The body of the loop
will be executed the first time through, whether the condition is true or false, as the
body of the loop is executed before the condition is tested. Post-test loops end when
the condition is true but they always do the loop at least once.
Remember: the post-test loop requires only one read statement but the pre-test
loop requires two. A very general rule is to use pre-test loops when the number of
loops is not known and post-test loops when the number of loops is known.
Analyse the example on the table below to understand the rules about how to write
post-test loops in both pseudocode and algorithms.
Table 5: POST TEST LOOP - Design an algorithm to cut the grass.
Pseudocode Solution
Algorithm Solution
REPEAT Use lawn mower
UNTIL grass is cut
In pseudocode the keywords
used for a post-test
repetition are REPEAT ...
UNTIL (see problem below).
The body of the loop is
underneath the REPEAT
keyword and the condition is
after the UNTIL keyword.
In a flowchart the post-test repetition is made with a
decision symbol and flowlines (see Figure 15.8). The
body of the loop is executed before the condition is
met in the decision symbol.
1. The pseudocode algorithm for a particular problem is given as:
Input the number 10 to 0 (in that order)
Read 2 numbers
WHILE both numbers >< 0
Calculate mean
Print mean
Read 2 numbers
Print end message
a. Write an explanation of this loop in general English.
b. When does the loop end?
c. Draw and complete the flowchart algorithm for the same problem.
2. A flowchart algorithm is provided for the problem ‘Making a Telephone
Call’ but there are errors. Correct the solution and then write the
pseudocode for the problem.
Incorrect Flowchart
Correct Flowchart
Correct Pseudocode:
6. Programming Languages
Once you have written the solution to the problem in either pseudo code or
flowcharts, you may begin your programming.
Programming languages are used to create the instructions in a program that can be
understood by the computer. Each programming language has its own set of rules
that must be strictly followed. The rules of the programming language are called its
syntax. Programming languages are divided into two groups:
Low Level Languages
High Level Languages
a. Low Level Languages
Low-level languages are the lowest level of computer languages and depend on the
hardware of the computer. Programs written using low-level languages are often
called machine code or assembly code. They process calculations much faster than
high-level languages.
The computer directly understands machine code. It can be executed or carried out
rapidly and no translation is needed. However, it is very difficult to write and most
people find it very hard to work with long strings of unstructured binary data or bit
streams such as ...00011011011100010 110010000111011...
b. High Level Languages
High-level languages use English-like codes where each statement corresponds to
several lines of machine code. Programming languages such as Java, Visual BASIC and
C++ are high-level languages. A compiler or interpreter translates a high-level
program into machine code so the computer can implement the solution.
An interpreter takes one instruction at a time and finds, from its instruction library,
the equivalent machine code instructions that it then obeys. Each time the program
is run, each instruction is translated into machine code making program execution
An incremental compiler is another type of interpreter that uses an interpreter for
the mainline of the program and compiles the modules as they are written. This
helps to speed up program execution.
A compiler changes the complete program from a high-level language into machine
code but does not execute the program until required. The translated program,
which is the one the computer understands, is kept for future use. This makes the
process quicker than when using an interpreter.
1. True or false?
a. Each programming language has the same rules that must be strictly
followed. ______
b. Most programmers use a high-level language. _______
c. A class describes how objects behave and the kind of information in
the object. _______
2. Explain the difference between a low-level language and a high-level language.
3. Explain why a compiler is a lot faster to use than an interpreter.
4. What is the purpose of a programming language?
7. Testing, Error Detection and Correction
Most programmers strive for the perfect program, however, few are able to achieve
it. It is rare for a complex program to be written without errors. Errors in a program
are called bugs. A bug is an error that makes the program run incorrectly. The
process of finding a bug is called debugging. Debugging is often a time- consuming
and challenging task.
a. Testing
Test data is used to detect and correct any potential errors in a program. Except for
simple programs, test data will only cover a small percentage of all the possible sets
of data. The programmer selects test data that will cater for the ‘worst-case’
situation. This is data the programmer predicts will cause a problem. It is often data
outside the boundaries of acceptable data such as entering a decimal number
instead of an integer. Test data is also designed to check for expected outcomes. For
example, if a user enters 4 the program should display the result for this value. The
selection of test data depends on the programmer’s understanding of the program.
Programmers use test data throughout the development of a program.
b. Error Types
To compile a program is to change the source code you have written into machine
code that the computer can understand. During the process, errors may be found in
the code.
Error detection involves identifying and describing the error. Error correction fixes
the source of the error to create a workable program. There are three basic types of
 Logic errors result from an incorrect series of steps to solve the problem. The
program with a logic error produces incorrect or unexpected results. Logic
errors can occur if the algorithm does not solve the problem correctly. The
algorithm should be tested before coding to eliminate logic errors. It is often
a difficult task to find and correct logic errors.
Syntax errors are made when the programmer has failed to follow the rules
(syntax) of the programming language. A syntax error may be a spelling error
or a symbol that cannot be translated. When the program is compiled or
interpreted, an error message will appear if the program contains any syntax
errors. Correcting any syntax errors is usually a simple task.
Run-time errors occur when it is impossible for the computer to carry out the
instruction. For example, if a calculation attempted to divide a number by
zero it would be a run-time error. The instruction has the correct syntax but it
is not possible to carry out the instruction. Incorrect data can often produce a
run-time error.
c. Error Detection and Correction
Software debugging tools are available for most programming languages. A
debugger is a program that will perform the desk check electronically. They
are often used with a breakpoint to watch the variables in a section of code.
Debuggers are only tools to find problems and do not provide the solution to
the problem.
Breakpoint is a roadblock in the execution of the program. When the
program reaches a breakpoint it stops. Breakpoints are useful in isolating
sections of the code and analysing them.
Desk checking involves the programmer checking each line of code. Desk
checking takes place after the algorithm has been written and again after it
has been coded in the programming language. The programmer executes the
program the same as the computer. Desk checking provides a way to see
exactly what code is being executed and the flow of execution through the
program. A desk check usually involves watching the variables. A list is
constructed containing the names of variables and their values. The list of
variables is updated after each step of the desk check. If somebody other
than the programmer performs the desk check it is called a peer check.
d. Desk Checking in Practice
Desk checking uses test data in a table to check all input and output. Test data should
include all the expected inputs and some unexpected input as well. Input test data is
used that will produce known results.
The test data should include:
1. Typical data, which will test the commonly used program paths;
2. Unusual but valid data, which will test the program paths used to process
exceptions; and
3. Incorrect, incomplete, or inappropriate data, which will test the program’s
error routines.
Examine the following problem to see how to perform a desk check.
An algorithm has been written to count the numbers from 1 to 5 and display them on
the screen. Test data for this problem needs no inputs but should show the expected
When the output does not match the expected output, there are one or more errors.
In this case, setting count to 0 at the start would solve the error. Another desk check
should be carried out to make sure.
1. What am I?
a. An error made when a programmer has failed
to follow the rules of programming.
b. An error that occurs when it is impossible for
the computer to carry out the instruction.
c. An error detection that involves putting a
roadblock in the execution of the program.
d. Documentation that involves writing an easyto-read program.
2. Complete the following sentences:
a. When a program is _______ an error
message will appear if the program contains
a syntax error.
b. A desk check usually involves watching the
c. A _______ is a program that will perform the
desk check electronically.
3. What is the purpose of test data?
4. Describe the three basic types of errors.
5. What is desk checking?
6. The following tables are provided to desk check the given algorithms.
Complete the tables.
8. Documentation
Documentation is a written description to explain the development and operation of
a program. It is not part of the actual code. Documentation is an important aspect of
writing programs as it helps the programmer to understand what is going on. It
should be written during the development of the program, however, it is often
neglected and left until last. This results in inadequate documentation making the
program difficult to understand and modify. The documentation required in a
program falls into three main categories:
Intrinsic documentation involves writing an easy-to-read program. It involves
using correct programming techniques and meaningful variable names such
as ‘height’ instead of ‘x’.
Internal documentation consists of any comments or remarks within the
program code to describe its purpose. The code below shows internal
documentation in REALBasic using double forward slash.
Sub Action()
St_message.textcolor=&cFF00FF // Changes text to colour Fuchsia
End Sub
External documentation consists of any written support material. This may
include a problem statement, input data, output data, processes, algorithm,
test data and a listing of the program, user manuals and installation guides.
1. Why is documentation an important aspect of writing programs?
2. Explain the difference between internal and external documentation.
3. Inadequate ________________ makes a program difficult to understand and
4. Edit the program below by inserting appropriate documentation in the right
hand column.
Set X to 0
Set Count to 1
Set X to X + 1
Print X
Increment Count by 1
Print Count
Powers, G. K. (2004) Information and Software Technology
Wilson, C. (2007) Exploring Information and Software Technology (4th ed)