introduction to computing dr. nadeem a khan. lecture 5

Introduction to Introduction to ComputingComputing

Dr. Nadeem A KhanDr. Nadeem A Khan

Lecture 5Lecture 5

On the web site On the web site http://suraj.lums.edu.pk/~cs101a0http://suraj.lums.edu.pk/~cs101a0

4/4/

Assignment 2 has been Assignment 2 has been posted. posted.

Chapter 3Chapter 3

Program PlanningProgram Planning

1.1. AnalyzeAnalyze

2.2. DesignDesign

3.3. Choose the Choose the InterfaceInterface

4.4. CodeCode

5.5. Test and DebugTest and Debug

6.6. Complete the Complete the DocumentationDocumentation

The Problem-Solving Process The Problem-Solving Process

Input

Processing

Output

Program Design ToolsProgram Design Tools

►Pseudo-codePseudo-code

►Flow ChartsFlow Charts

►Hierarchy Hierarchy ChartsCharts

Postage stamp problem:Postage stamp problem:

How many stamps to put on a How many stamps to put on a envelop given one stamp is envelop given one stamp is needed for every five sheets of needed for every five sheets of paper or a fraction thereofpaper or a fraction thereof

PseudocodePseudocode

►Abbreviated version of actual Abbreviated version of actual computer code in English-like computer code in English-like statementsstatements

Pseudo code: Postage Stamp Pseudo code: Postage Stamp ProblemProblem

►Program – Determine the number of Program – Determine the number of stamps for a letterstamps for a letter

Read SheetsRead Sheets

Set the number of stamps to sheets / 5Set the number of stamps to sheets / 5

Round the number of stamps Round the number of stamps

Display the number of stamps Display the number of stamps

FlowchartsFlowcharts

►Special geometric symbols Special geometric symbols connected by arrows connected by arrows

Postage Postage stamp stamp

problemproblem

Start

Read sheets

Set stamps = sheets/ 5

Display stamps

Round stamps up to next

whole number

End

input

processing

output

processing

Elements of FlowchartsElements of Flowcharts

Symbol Name

Flowline

Terminal

Input/Output

Processing

Decision

Continued…Continued…

Symbol Name

Connector

Off page Connector

Predefined process

Annotation

Hierarchy chartHierarchy chart

►Shows overall program structureShows overall program structure

Hierarchy Charts: Postage Hierarchy Charts: Postage Stamp ProblemStamp Problem

Postage Stamp

Problem

Read

Sheets

Calculate

stamps

Display

stamps

Set stamps = sheets/5

Round stamps to next whole

number

Another problem:Another problem:

Given a street number of one-way Given a street number of one-way street in New York, decide the street in New York, decide the direction of the street, either direction of the street, either eastbound or westboundeastbound or westbound

Note: Note: Even numbered street: EastboundEven numbered street: EastboundOdd numbered street: WestboundOdd numbered street: Westbound

DecisionsDecisions

►Sequence StructureSequence Structure – a sequence – a sequence followed without skipping any line.followed without skipping any line.

►Decision StructureDecision Structure – a structure – a structure which requires a decision for any lines which requires a decision for any lines of code to be executed.of code to be executed.

Decision Structure: Decision Structure: PseudocodePseudocode

IF condition is TRUE THENIF condition is TRUE THENProcess step(s) 1Process step(s) 1

ELSEELSE Process step(s) 2Process step(s) 2

END IFEND IF

Decision Decision Structure:Structure:FlowchartFlowchart Process

Step (s) 2

Is Condition True

Process Step (s)

1

Decision Structure: Decision Structure: PseudocodePseudocode

What in case of multiple What in case of multiple conditions?conditions?

Decision Structure: Decision Structure: PseudocodePseudocode

IF condition 1 is TRUE THENIF condition 1 is TRUE THENProcess step(s) 1Process step(s) 1

ELSE IF condition 2 is TRUE ELSE IF condition 2 is TRUE THENTHEN Process step(s) 2Process step(s) 2

ELSEELSEProcess step(s) 3Process step(s) 3

END IFEND IF

Pseudo-Code: Street Direction Pseudo-Code: Street Direction ProblemProblem

Get Street

IF Street is EVEN

Display Eastbound

ELSE

Display Westbound

END IF

Flow Flow Chart: Chart: Street Street DirectioDirectionnProblem Problem

End

Start

Get Street

Is street even?

Display Westbound

Display Eastbound

Hierarchy Chart: Street Hierarchy Chart: Street Direction ProblemDirection Problem

Street Directio

n Program

Get Street

Number

Decide whether street

number is odd or even

Display direction

Still Another ProblemStill Another Problem

► CCalculate and report the grade-point alculate and report the grade-point average of a class.average of a class.

The Loop StructureThe Loop Structure

► A programming structure that A programming structure that executes instructions many times.executes instructions many times.

Flow chart: Flow chart: loop structureloop structure No

Process Step(s)

Is condition true ?

Yes

Pseudo code: loop structurePseudo code: loop structure

► DO WHILEDO WHILE condition is TRUE condition is TRUE

Process Step(s)Process Step(s)

LOOPLOOP

Draw the Flowchart for the class Draw the Flowchart for the class average problemaverage problem

Pseudo code: Class Average Pseudo code: Class Average ProblemProblem

INITIALIZE Counter and Sum to 0

DO WHILE there are more data

Get the next Grade

Add the Grade to the Sum

Increment the Counter

LOOP

Compute Average = Sum/Counter

Display Average

Hierarchy Chart: Class Average Hierarchy Chart: Class Average ProblemProblem

Class average program

Get grade

Compute sum

Display average

Calculate

average

Chapter 4Chapter 4

► Already known:Already known:

StringString

SingleSingle

IntegerInteger

Data TypesData Types

► StringsStrings

Storage:Storage: 10 bytes + string length10 bytes + string length

Range:Range: 0 to app. 2 billions chars. 0 to app. 2 billions chars.

Declaration:Declaration:

Dim strVarLen As String Dim strVarLen As String

((declares a string of a variable declares a string of a variable length)length)

Data Types Data Types (Contd.)(Contd.)

► Fixed-Length StringsFixed-Length Strings

Storage:Storage: Length of stringLength of string

Range:Range: 1 to app. 65, 400 chars. 1 to app. 65, 400 chars.

Declaration:Declaration:

Dim strFixLen As String * 2Dim strFixLen As String * 2

(declares a string of a fix size of 2 (declares a string of a fix size of 2 chars.)chars.)

Data Types (Contd.)Data Types (Contd.)

► Fixed-Length StringsFixed-Length StringsUsage: Usage:

ExampleExampleDim strText As String * 5Dim strText As String * 5

Let strText = “Hello” Let strText = “Hello” Picture1.Print strTextPicture1.Print strTextLet strText = “H” Let strText = “H” Picture1.Print strTextPicture1.Print strTextLet strText = “HelloWorld” Let strText = “HelloWorld” Picture1.Print strTextPicture1.Print strText

Data TypesData Types

► Fixed-Length StringsFixed-Length StringsUsage: Usage:

Result:Result:HelloHello (Complete string) (Complete string)

H…. H…. (H followed 4 spaces)(H followed 4 spaces)

HelloHello (First 5 characters (First 5 characters only)only)

=> The length is fix=> The length is fix

Data TypesData Types

► IntegersIntegers

Storage:Storage: 2 bytes2 bytes

Range:Range: -32,768 to 32,767 -32,768 to 32,767

Declaration:Declaration:

Dim intExample As IntegerDim intExample As Integer

(declares intExample as an Integer (declares intExample as an Integer variable)variable)

Data Types Data Types (Contd.)(Contd.)

► IntegersIntegersUsage: Usage:

ExampleExampleDim count As IntegerDim count As IntegerLet count= 6 Let count= 6 Picture1.Print countPicture1.Print countLet count= count+1Let count= count+1Picture1.Print countPicture1.Print countLet count= 6/5 Let count= 6/5 Picture1.Print countPicture1.Print countLet count= 2.33333 * 2Let count= 2.33333 * 2Picture1.Print countPicture1.Print count

Data TypesData Types

► IntegerIntegerUsage: Usage:

ResultResult667 7 1 1 (rounding to lower value)(rounding to lower value)55 (rounding to higher value)(rounding to higher value)

=> takes only whole number values=> takes only whole number values

Data TypesData Types

► Long (Integer)Long (Integer)

Storage:Storage: 4 bytes4 bytes

Range:Range: -2,147,483,648 to -2,147,483,648 to 2,147,483,647 2,147,483,647

Declaration:Declaration:

Dim lngExample As LongDim lngExample As Long

(declares lntExample as a long variable)(declares lntExample as a long variable)

Data Types Data Types (Contd.)(Contd.)

► Long (Integer)Long (Integer)

Usage:Usage: Same as Integer Type except the Same as Integer Type except the range isrange is

much largermuch larger

Data Types Data Types (Contd.)(Contd.)

► ByteByte

Storage:Storage: 1 byte1 byte

Range:Range: 0 to 255 0 to 255

Declaration:Declaration:

Dim bytExample As ByteDim bytExample As Byte

(declares bytExample as a Byte type (declares bytExample as a Byte type variable)variable)

Data Types Data Types (Contd.)(Contd.)

►ByteByte

Usage:Usage: Same as Integer Type except the Same as Integer Type except the range isrange is

positive and much smallerpositive and much smaller

Data Types Data Types (Contd.)(Contd.)

► BooleanBoolean

Storage:Storage: 2 bytes2 bytes

Range:Range: TRUE(1) or FALSE(0) TRUE(1) or FALSE(0)

Declaration:Declaration:

Dim blnState As BooleanDim blnState As Boolean

(declares a Boolean type variable (declares a Boolean type variable blnState)blnState)

Data Types Data Types (Contd.)(Contd.)

► BooleanBooleanUsage: Usage:

ExampleExampleDim blnExample As BooleanDim blnExample As BooleanLet blnExample= FALSE Let blnExample= FALSE Picture1.Print blnExamplePicture1.Print blnExampleLet blnExample= 1Let blnExample= 1Picture1.Print blnExamplePicture1.Print blnExampleLet blnExample= 6Let blnExample= 6Picture1.Print blnExamplePicture1.Print blnExample

Let blnExample= -8*7+5.2Let blnExample= -8*7+5.2Picture1.Print blnExamplePicture1.Print blnExample

Data Types Data Types (Contd.)(Contd.)

► BooleanBooleanUsage: Usage:

ExampleExample FALSEFALSE

TRUETRUE

TRUETRUE

TRUETRUE

=>Values other than 0 are TRUE=>Values other than 0 are TRUE

Data Types Data Types (Contd.)(Contd.)

► Single (Precision Floating-Point)Single (Precision Floating-Point)

Storage:Storage: 4 bytes4 bytes

Range:Range: -3.4…E38 to -1.4…E-45 -3.4…E38 to -1.4…E-45 (negative) (negative)

1.4…E-45 to 3.4…E38 (positive)1.4…E-45 to 3.4…E38 (positive)

Declaration:Declaration:

Dim sngAverage As SingleDim sngAverage As Single

(declares a Single type variable sngAverage)(declares a Single type variable sngAverage)

Data Types Data Types (Contd.)(Contd.)

► Double (Precision Floating-Point)Double (Precision Floating-Point)

Storage:Storage: 8 bytes8 bytes

Range:Range: -1.7…E308 to -4.9…E-324 (negative) -1.7…E308 to -4.9…E-324 (negative)

4.9…E-324 to 1.7…E308 (positive)4.9…E-324 to 1.7…E308 (positive)

Declaration:Declaration:

Dim dblAverage As DoubleDim dblAverage As Double

(declares a Double type variable dblAverage)(declares a Double type variable dblAverage)

Data Types Data Types (Contd.)(Contd.)

► DoubleDoubleUsage: Usage:

ExampleExampleDim sngValue As Single, dblValue As DoubleDim sngValue As Single, dblValue As Double

Let sngValue= 1/3 Let sngValue= 1/3

Picture1.Print sngValuePicture1.Print sngValue

Let dblValue= 1/3Let dblValue= 1/3

Picture1.Print dblValuePicture1.Print dblValue

Data Types Data Types (Contd.)(Contd.)

► DoubleDoubleUsage: Usage:

ResultResult0.33333330.3333333 (Single precision)(Single precision)

0.333333333333333 (Double precision)0.333333333333333 (Double precision)

=> Value of 1/3 represented more => Value of 1/3 represented more accuratelyaccurately

by double than by single by double than by single

Data Types Data Types (Contd.)(Contd.)

► DoubleDoubleUsage: Usage:

ExampleExampleDim sngValue As Single, dblValue As Dim sngValue As Single, dblValue As

DoubleDouble

Let sngValue= 1/3Let sngValue= 1/3

Let sngValue= sngValue * 100000 Let sngValue= sngValue * 100000

Picture1.Print sngValuePicture1.Print sngValue

Let dblValue= 1/3Let dblValue= 1/3

Let dblValue= dblValue * 100000 Let dblValue= dblValue * 100000

Picture1.Print dblValuePicture1.Print dblValue

Data Types Data Types (Contd.)(Contd.)

► DoubleDoubleUsage: Usage:

ResultResult33333.3433333.34 (Single precision; rounding error)(Single precision; rounding error)

33333.3333333333 (Double precision)33333.3333333333 (Double precision)

=> - The decimal point is floating;=> - The decimal point is floating;

- Eventually both will be subjected to rounding errors- Eventually both will be subjected to rounding errors

value increases to large valuesvalue increases to large values

- Still Double will remain more precise than Single - Still Double will remain more precise than Single

Data Types Data Types (Contd.)(Contd.)

► CurrencyCurrency

Storage:Storage: 8 bytes8 bytes

Range:Range: -922,337,203,685,477.5808 to -922,337,203,685,477.5808 to

922,337,203,685,477.5807 922,337,203,685,477.5807

Declaration:Declaration:

Dim curRevenue As CurrencyDim curRevenue As Currency

(declares a Currency type variable (declares a Currency type variable curRevenue)curRevenue)

Data Types Data Types (Contd.)(Contd.)

► CurrencyCurrencyUsage: Usage:

ExampleExampleDim curValue As CurrencyDim curValue As Currency

Let curValue= 1/3Let curValue= 1/3

Picture1.Print curValuePicture1.Print curValue

Let curValue= 100*1/3 Let curValue= 100*1/3

Picture1.Print curValuePicture1.Print curValue

Data Types Data Types (Contd.)(Contd.)

► CurrencyCurrencyUsage: Usage:

ResultResult0.33330.3333

33333.3333 33333.3333

=>=> - The decimal point is NOT floating;- The decimal point is NOT floating;

- Could be used for currency and scientific - Could be used for currency and scientific research research

- No rounding problems for high values- No rounding problems for high values

Data Types Data Types (Contd.)(Contd.)

►Even more data types Even more data types Date Variable: for date and timeDate Variable: for date and time Object VariableObject Variable Variant VariableVariant Variable ………………..

Read the book for more info.Read the book for more info.

Data Types Data Types (Contd.)(Contd.)

Local vs Form VariablesLocal vs Form Variables