Post on 03-Jan-2016
Software Development Topic 3
High Level Language Constructs
Resources
Theory for the unit is covered in pages of How to Pass Higher Computing
Throughout this topic you will be asked to complete practical tasks from the Software Development Using Visual Basic booklet
What you need to know
Description and exemplification of a number of programming construct
Features of high level languages Outline in pseudocode of high level language
constructs
Re-cap – What you already know about data types
A variable is used to store data in a program Variables can be of different types and must be
declared at the start of the program String Real Integer Boolean
Each data type has different memory requirements Declaring the data type allows a translator to
allocate the correct amount of memory
Variable types used in Visual Basic
Integer – Whole numbers from about -32,000 - +32,000
Long – Whole numbers from about -2,000,000,000 - +2,000,000,000
Single – Fractional numbers Double – Fractional numbers with more accuracy String – Text or words Boolean – Can have only 2 values T/F, Y/N, M/F
Practical Activity – 3 blocks
Complete the practical activities for Topic 1 from the practical booklet. This is a revision topic and should be completed quickly
Practical Software Development Topic 2
Strings and Branches
What we will learn
Enforced variable declarations String Functions
Enforced Variable Declarations
You can set up visual basic to make sure you declare your variables in every program.
If you do not declare your variables your program will not work correctly
Tools, Options, Editor, Required Variable Declaration
String Functions
LEN Ucase Lcase Asc Chr$
Each of these functions performs a task on a string. You will work out what each function does by creating a test program
Practical Activity – 1 block
Beginning at Topic 2 read pages 1 – 5 Create the function test programs detailed on
pages 6-7 – section 2.5
Report back by typing up a table of testing for each function. You should then write a sentence explaining what each function does. (bottom of page 7)
Parts of strings are extracted and used elsewhere in the program
Extracts letters from the middle of a string
Word = Computing, is, funKeyword = Mid$(word, 7,5)PRINT Keyword
What would the output of this program be?
String Operations - Substrings
Word = Computing is funMid$(word, 7,5)PRINT Mid
The code Mid$(word, 7,5) extracts 5 characters from the string variable called word, starting with the 7th character. That means the output would be
ing i
Remember a space counts as a character
String Operations - Concatenation
Concatenations means adding two strings together
LET part1 = Man
LET part2 = Chester
LET whole = part1 & part2
PRINT whole
What would be the output of this program?
Practical Activity
Beginning on page 9 of Unit 2 in your practical software development book work through the practical task 2.7 – Devising User IDs
Analysis and Design has been done for you Implementation has been party done You are wholly responsible for testing and
evaluation Submit printouts for implementation, testing
and evaluation
Practical Assessment
Well done you are now ready to complete your first practical assessment.
This will be done under assessment conditions.
You may refer to previous programs you have created or to your programming manual
You will be observed throughout the task First Practical Assessment
Past paper questions on string operations
A string variable mystring contains the word “elephant”. Using code from a programming environment with which you are familiar, show how you would extract the substring “ant” from mystring? 2006 paper, Q 4(b)
3 marks Describe what is meant by the string operation
concatenation. 2006 paper, Q 4(a)
1 mark
Suggested Solutions
Mid$(mystring, 6,3) extracts 3 characters from the string variable called mystring, starting with the 6th character. That means the output from mystring “elephant” would be “ant”
1 mark for Mid$ function1 mark for starting point (6)1 mark for 3 characters (3)
Concatenation is the process of joining strings together
1 mark
Formatting of Input and Output
You should be familiar with writing programs using different input and output formats. Visual basic has a range of input and output formats Text boxes List boxes Radio buttons Image boxes
It is not necessary for you to be able to use all of these but you should be aware of them
Multiple Outcome Selection Selection is used when a choice has to be made in a
program. The simplest form of selection uses an IF statement
IF MARK>=70 thenPRINT “A”ELSE IF MARK >=60 THENPRINT “B”ELSE IF MARK >= 50 THENPRINT “C”ELSE IF MARK >=45 THENPRINT”D”ELSEPRINT “No Award”END IF
CASE STATEMENT
CASE mark
>= 70 PRINT “A”
>=60 PRINT “B”
>=50 PRINT “C”
>=45 PRINT “D”
CASE ELSE PRINT “No Award”
Repetition in Programs
Fixed Loops – for ……….. Next Do …… Loop Until Do Until …….. Loop Do …… Loop While ……. Do While ……. Loop
Practical Activity – 1 block max
To ensure your understanding of loops (repetition) and selection (IF and CASE) you should chose 2 programs from 2.8 – 2.11 which you should implement and test.
Submit a structured listing for each program you implement
Topic 3
Loops (Revision)
Revision
Remember we have already covered loops during Standard Grade so the following programs should be done as quickly as possible.
Practical Activity – 2 blocks max
Revise counters by doing example 3.6.1 & 3.6.3 Revise for …. next loops by doing example 3.7 Revise Do …. Loop Until by doing example 3.12 Consolidate your learning by doing example 3.12.2
For each program you should submit a structured listing
For one program you should also submit analysis, design, test table with screen shots and produce a user guide, technical guide and evaluation
Homework Exercise
Complete homework exercise revising points covered so far
Topic 4
1 Dimensional Arrays
Arrays
The same type of data grouped together is called an array
The array is given a meaningful name Each part of the array is called an element Each element is given a unique number
Declaring arrays
You must declare the name and the number of elements in an array
DIM name(9) as stringDIM mark(9) as integer
This tells the program the dimension of the array – ie the number of elements
Using Arrays in Visual Basic
Visual basic array’s always start with element number 0
To set up an array to hold 5 names you would declare as follows
DIM pupil_name(4) As String
This instructs visual basic to set aside 5 elements to store 5 names
(Filling an array with 6 numbers entered by the user)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Number(0) Number(1) Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
0
Number(0) Number(1) Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
0
Numbers(0) = inputbox(“ Please enter a number”)
Number(0) Number(1) Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
0
Number(0)
8
Number(1) Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
0
Number(0)
8
Number(1) Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
1
Number(0)
8
Number(1) Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
1
Numbers(1) = inputbox(“ Please enter a number”)
Number(0)
8
Number(1) Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
1
Number(0)
8
Number(1)
12
Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
1
Number(0)
8
Number(1)
12
Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
2
Number(0)
8
Number(1)
12
Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
2
Numbers(2) = inputbox(“ Please enter a number”)
Number(0)
8
Number(1)
12
Number(2) Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
2
Number(0)
8
Number(1)
12
Number(2)
1
Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
2
Number(0)
8
Number(1)
12
Number(2)
1
Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
3
Number(0)
8
Number(1)
12
Number(2)
1
Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
3
Numbers(3) = inputbox(“ Please enter a number”)
Number(0)
8
Number(1)
12
Number(2)
1
Number(3) Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
3
Number(0)
8
Number(1)
12
Number(2)
1
Number(3)
21
Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
3
Number(0)
8
Number(1)
12
Number(2)
1
Number(3)
21
Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
4
Number(0)
8
Number(1)
12
Number(2)
1
Number(3)
21
Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
4
Numbers(4) = inputbox(“ Please enter a number”)
Number(0)
8
Number(1)
12
Number(2)
1
Number(3)
21
Number(4) Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
4
Number(0)
8
Number(1)
12
Number(2)
1
Number(3)
21
Number(4)
17
Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
4
Number(0)
8
Number(1)
12
Number(2)
1
Number(3)
21
Number(4)
17
Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
5
Number(0)
8
Number(1)
12
Number(2)
1
Number(3)
21
Number(4)
17
Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
5
Numbers(5) = inputbox(“ Please enter a number”)
Number(0)
8
Number(1)
12
Number(2)
1
Number(3)
21
Number(4)
17
Number(5)
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
5
Number(0)
8
Number(1)
12
Number(2)
1
Number(3)
21
Number(4)
17
Number(5)
5
Dim Numbers(5) as integer For counter = 0 to 5
Numbers(counter) = inputbox(“ Please enter a number”)
Next counter
Counter
5
Number(0)
8
Number(1)
12
Number(2)
1
Number(3)
21
Number(4)
17
Number(5)
5
Glossary Definitions
At the back of your jotter write a glossary definition of
Array Element
Practical Activity
You should now complete Topic 4 from the practical booklet
Modularity
Code should be broken into manageable sections.
Visual basic used two ways of breaking up a program Subroutines Functions
Subroutines
Sections of code which do a specific task Can be called during the running of the
program
Functions
A function is a sub-program which returns a result
Functions can be pre-defined or user-defined Pre-defined functions we have already met:
LEN RND UCASE LCASE
User defined functions
You must know The name of the function The type of result it will return What input data is needed (type)
Benefits of User defined functions
Keeps main code simpler and more readable Same function can be reused elsewhere in
the code Can be saved in a module library
Functions
Like a subroutine but has a value which can be assigned to a variable
These variables can be Local variables Global variables
Practical Activity Complete the practical activities for Topic 5 this is
straight forward topic and should be completed quickly
5.5.1 5.5.3 Either 5.5.4 or 5.5.5 5.5.6 – full analysis, design, implementation, testing
and evaluation (all but implementation and testing can be done at home)
If you cannot complete all of this within class time you must catch up at home
Written Questions
Answer questions 23 – 26 on pages 57 and 58 of How to pass Higher Computing
Complete Homework Revision Ex 2
Section 6
Modular Programming
Real life programming
Examples so far have been short, simple programs
Higher level programming requires the use of modules and parameters
Using variables in Higher programming
You need to be familiar with and be able to use the following types of variables Local variable Global variable Variables (parameters) passed by reference Variables (parameters) passed by value
Local Variables
We have already used local variables in the functions we created earlier
A local variable is defined for use in one part of a program
It can only be assigned a value inside a procedure, sub-routine or function
Using local variables reduces the chances of a variable being changed accidentally if the same variable is used in other parts of a program
Global Variables
Can be assigned a value anywhere in a program
Should only be used for data that needs to be shared between different procedures
Should be used with care due to the fact that they have the ability to change a value throughout a whole program
Glossary Definition
At the back of your jotter write a glossary definition for Variable Local Variable Global Variable
Data Flow
Variables which represent data can be used in many different parts of a program
Programs are divided into sub-routines (also called modules)
The movement of data between subroutines is controlled by using Parameters
Parameters
A parameter is a variable or value that is passed into or out of a subroutine.
Parameters are used to control data flow in a program
When a subroutine is used within a program, the calling program must pass parameters to it. This is called Parameter Passing
Practical Task
Create the program on pages 5 – 7 of your practical booklet (Topic 6) 6.5.1
Parameter Passing
Parameters can be passed (called):
Called/Passed by Reference or
Called/Passed by Value
Passed by Value (in)
The current value is passed into the subroutine
Any changes made do not affect the program Used when the variable content does not
need passed out.
The actual variable is passed into the subroutine
The variable may be updated and the new value passed out.
Used when the variable content needs to be passed out.
Pass by Reference (out)
Diagram: Data Flow
Area of Rectangle
Enter Length
Enter Breadth
Calculate Area
Display Area
OUT: breadth OUT: areaIN: length
length
breadth
area
PARAMETERS
OUT: length IN: breadth IN: area
Algorithm showing Data Flow
1. Get length of rectangle (OUT: length)
2. Get breadth of rectangle (OUT: breadth)
3. Calculate the area (IN: length,breadth OUT: area)
4. Display the area (IN: area)
Glossary definitions
At the back of your jotter, write a glossary definition of
Passing a parameter by reference Passing a parameter by value
Using a structured chart to show data flow
Your teacher will take you through the data flow diagram on pages 8 – 10
An alternative method is shown on pages 10 - 11
6.5.2.2
You should now add the parameters to the code you created earlier
Exemplar 1 (Parameter Passing)
Software Specification
Design, implement and test a program that will ask the user to enter the radius and height of a cylinder. The volume will then be calculated and displayed.You should use a structured chart to show the data flow before you do the algorithm in pseudocode
Diagram: Data Flow
Volume of Cylinder
Get Input Calculate Volume
Display Volume
OUT: height OUT: VolumeIN: radius
radius
height
volume
PARAMETERS
OUT: radiusIN: height
IN: Volume
Exemplar 1Algorithm (With Data Flow)
1. Declare Variables2. Get Input Out: radius, height
2.1 Get and store Radius2.2 Get and store Height
3. Calculate Volume in: radius, height
out: Volume
3.1 Volume = 3.14*radius*radius*height
4. Display Volume in: Volume
4.1 Display Volume of the cylinder
Implementation – Main Program
Private Sub CmdRun_Click()
!Declare the variables – Step 1. of Algorithm
Dim radius As Single, height As Single, Volume As Single
!Main part of the program – Steps 2. 3. & 4.of Algorithm
Call Get_input (radius, height)
Call Calculate_Volume (radius, height, Volume)
Call Display_Volume (Volume)
End
Sub Routines – refinements of Algorithm
Private Sub Get_input (ByRef radius As single, height As single)
radius = InputBox ("Enter the radius") (step 2.1 of algorithm)
height = InputBox ("Enter the Height") (step 2.2 of algorithm)
End Sub
Private Sub Calculate_Volume(ByVal radius as Single, height As Single, ByRef Volume as Single)
Volume = 3.14 * radius * radius * height (step 3.1 of algorithm)
End Sub
Private Sub Display_Volume(ByVal Volume As Single)
PicDisplay.Print Volume (step 4.1 of algorithm)
End Sub
Exemplar 2 (Parameter Passing)
Using the previous example complete the following task
Design implement and test a program that will ask the user to enter the distance travelled and the time taken for a journey. The speed will then be calculated and displayed.
Exemplar 3 (Parameter Passing)
Software Specification
Design, implement and test a program that will ask the user to enter the name of a pupil followed by four exam marks (out of 100). The average mark will then be calculated and the pupil name and average mark should be displayed.
Exemplar 3 – Suggested Solution
Data flow is important to ensure
correct data types are used data does not get mixed up in a
program data only gets changed if desired the correct data is used in the correct
sub-routine (module)
Homework Exercise 3
Practical Activity
To ensure you understand what happens in a program when a program is passed by value or passed by reference you should complete practical task 6.6.1 and 6.6.2
Actual and Formal Parameters
Past paper questions on variables
A program uses global variables and local variables. Explain each of these terms. (2006 Past Paper, Q5)
2 marks
Suggested answer
Past paper question (2002, Q18)A program is used to analyse the number of road
traffic accidents in six areas. The names of the areas and the number of accidents are stored in 2 separate arrays. Here is a possible algorithm for the part of the program which finds the area with highest number of accidents
2. Find area with highest number of accidents2.1 find position of maximum number of
accidents in the array2.2 print name from corresponding position in
area array
Part (a) of question
Step 1 requires 2 parameters. Identify these parameters and state their data types and methods of parameter passing
Break this question down before attempting to answer it
identify the parameters
state their data types
state methods of parameter passing
Suggested solution part (a)
A variable to store the position of the maximum number of accidents will be needed (Position)
As this variable will store the position of the variable maximum the variable must be a whole number therefore the data type must be an integer
It is presumed the position must be passed to other parts of the program (eg display) so therefore this variable should be passed by reference
Written Task
Answer questions 17 – 22 on page 57 of How to Pass Higher Computing
End of Topic Activities
Complete end of topic evaluation sheet Complete end of topic ActiVote Assessment
Learning Outcomes - High level programming language constructs
Description and exemplification of the following constructs in pseudocode and an appropriate high level language: string operations (concatenation and substrings), CASE (or equivalent multiple outcome selection)
Description and exemplification of real, integer and boolean variables; and 1-D arrays
Description and exemplification of procedures/subroutines/subprograms, user-defined functions,
modularity, parameter passing (in, out, in/out), call by reference/value, local and global variables, scope of a variable