Mr C Johnston ICT Teacher BTEC IT Unit 06 - Lesson 05 Learning To Program.

Mr C JohnstonICT Teacher

www.computechedu.co.uk

BTEC IT Unit 06 - Lesson 05

Learning To Program

http://www.computechedu.co.uk/

Session Objectives

Understand the concept of variables in programs and appreciate their use and properties,

Understand different programming constructs which can be used to structure programs,

Use different program constructs to create small programs to illustrate their use.

Variables All programs at some point will need to store data which is either input or

from processing, Although programs often output data to a more permanent form the data

still needs to be stored somewhere within the program prior to this, Data is temporarily stored within in a program in a VARIABLE, Variables all have a name and a data type, and need to be defined within

the program before they can be used.

Dim studentName As String

Declares the variable Names the variable Set the data type of the variable

Variable Names When I first started to program we called variables X and Y as name

length was limited – hard to tell what they are, Good programming technique now is to use sensible names for our

variables to make the code easy to read and maintain, Most language don’t all spaces in variable name so often we use

capital letters (studentName) or underscores (student_Name) instead.

Variable Data Types As well as being declared and having a name a

variable needs a data type, The data type refers to the type of data which will be

stored within the variable. Typical data types used include:Data Type Data Use Range of Values

Boolean Values that can be true or false

True or False

Byte Whole numbers (8 bit) 0 to 255

Integer Whole numbers (16 bit) -32,768 to +32,767

Long Large whole numbers c +/- 2x109

Single Decimal numbers (float) Up to 7 significant figures

Double Large decimal numbers Up to 14 significant figures

Date Date and Time Variety of date and time formats

String Any type of character Sometimes char limit

VbMsgBoxResult

Results of msgbox button presses

vbYes, vbNo, vbOK, vbCancel etc

Programming Constructs

There a several different programming constructs which make up the structure of a program:

Sequence Statements: When the program statements are followed one after another

Selection (or decision): When a choice is made based on criteria – usually IF

statements Iteration (or repetition):

When a section of code is repeated using a loop – there are two main types of loop fixed (repeat until) and conditional (while do)

Visual Basic for Applications1

Overview To demonstrate some of the programming constructs

we are going to use a programming language built into PowerPoint called Visual Basic for Applications (VBA),

To access VBA you can either press Alt+F11 or click on the Visual Basic Icon from the developer ribbon.

To start programming within visual basic you first need to create a new module and then define a subroutine or a function to house the code,

Subroutine and function names can be anything sensible as long as there are no spaces and a reserved word is not used,

Code is then added between the Sub and the End Sub to make the program.

Code added here


Modules, Subs and Functions

To declare a variable in visual basic we use the DIM statement.


Declaring Variables

Dim [variable name] As [variable type]Data Type

Boolean

Byte

Integer

Long

Single

Double

Date

String

VbMsgBoxResult

Assign data to a variable:[variableName] = [value]

Output to screen:MsgBox(“[message]”) OR MsgBox([variableName])

Input value into program:[variableName] = InputBox(“[instruction]”)

Concatenate variables and data:[variableName] = “[message] ” & [variableName] & “ [message]”


Sequence Statements1

Mathematical Operators – As well as concatenating variables we can also manipulate them using mathematical operators.

[variableName] = [variableName] [mathsOperator] [variable OR value]


Sequence Statements2

Operator

Data Use Example Order of Precedence

^ Raise to power of 3 ^ 3 = 27 1

* Multiply 6 * 4 = 24 2

/ Division 50 / 5 = 10 3

Mod Remainder of division

10 MOD 3 = 1 4

+ Add 123 + 33 = 156 5

- Subtract 83 – 47 = 36 6

IF statements are used to check if a condition has been metIf [condition] Then

[instructions to be run if true]Else

[instructions to be run if false]End If


Selection Statements1

IF statements can be nested to test if different conditions have been metIf [condition] Then

[instructions to be run if true]Else IF

[instructions to be run if true]Else IF

[instructions to be run if both false]End If



Nested IF statements although useful are quite inefficient, and its better to use a SELECT CASE statementSelect Case [variable to be used]

Case Is [condition][instructions if true]



etcEnd Select



When creating IF and CASE statements we use operators to construct conditions,

Relational operators allow use to construct conditions which compare variables with other values,

Logical operators can be used to combine different conditions.


Logical and Relational Operators

Operator Meaning

> Greater than

< Less than

/ Equal to

>= Greater than or equal to

<= Less than or equal to

<> Not equal to

Operator

Meaning Example

AND Returns true if all conditions are true

Age > 18 AND Gender=‘F’

OR Returns true if one of the conditions is true

Age > 18 OR Gender=‘F’

NOT Returns the opposite of the condition

NOT Age > 18

Iteration means repeat or loop, There are two different types of loop we use within

programming: Fixed loops – repeat for a fixed number of times Variable loops – repeat until criteria are met


Iteration1

FOR loops repeat a section of code a stated number of timesFOR [counter variable] = [start value] to [end value]

[instructions to be run inside loop]Next


FOR Loops

DO loops keeping repeating the instructions until a criteria has been met.

Criteria could be WHILE, or UNTILDO WHILE [variable] [criteria]

[instructions to be run inside loop]Loop

DO UNTIL [variable] [criteria][instructions to be run inside loop]

Loop


DO Loops

Mr C Johnston ICT Teacher BTEC IT Unit 06 - Lesson 05 Learning To Program.

Documents

type of data

variable data typesas

typical data types

different program constructs

program statements

visual basic icon

dovisual basic

herevisual basic