ACSE 20068th Conference

The Iconic Programmer

Stephen Chen

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Overview

Actual slides from first three weeks Want students to focus on

programming concepts rather than (JAVA) syntax

Want students to learn to think in structures (i.e. problem solve)

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Structured Programming

Focus on processes – focus on actions 3 structures of structured programming

SequencePerform an action

BranchSelect an action (or no action)

LoopRepeat an action

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Each structure has an icon

Program by assembling icons

Iconic Programmer

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Sequence

Standard operation of a computer Actions are performed in sequence

First actionSecond action…Last action

Program runs same way each time

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Actions

ActionManipulate data

Iconic ProgrammerDeclareAssignOutput

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Declarations

A computer needs to allocate storage space for all data that it manipulatesDeclaration gives a meaningful name to

the data element/storage space Iconic Programmer

Only integer data elementsGive name in text box

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Assignments

Once the computer has a storage space, it can store/change data in that space

Iconic ProgrammerRandom valueResult of mathematical expressionUser input

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Mathematical Expressions

value = value +1 (math)The value is equal to the value plus one Impossible mathematically

value = value + 1 (computers)The storage space for value will become

the previous contents plus one Actions: perform math, perform storage

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Output

When computer is done with program (or during debugging), we may want to see the result – what is in a storage space

Iconic ProgrammerValue in storage spaceText information (nominally stored)

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Sample Program

Output the double and triple of an inputDeclare a storage spaceAssign an input value to the storage spaceDeclare a second storage spaceAssign double the input to this spaceOutput the value in the second spaceAssign triple the input to this spaceOutput the value in the second space

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Branching allows a program to make decisions

Diamonds represent conditionsTwo outgoing paths from conditionPaths (with sequences) can be skipped

Branching

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Example of Branching

Program specificationMake withdrawal if funds are sufficient

Program actionsCheck account balance and withdraw

amountMake withdrawal

Need to make withdrawal optional

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Decisions

Branching selects from two paths Two paths two states

true (yes)false (no)

Diamond contains a condition A condition is a true-false question

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Relational Operators

How to turn integers into true/false?Greater thanLess thanEqual toNot equal toGreater than or equal toLess than or equal to

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Compound Conditions

Allow us to put two (or more) sub-conditions into a conditionANDOR

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AND

The expression is TRUE if and only if both input variables are TRUE

TRUE

1

FALSE

0

TRUE

1

TRUE

1

FALSE

0

FALSE

0

FALSE

0

FALSE

0

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OR

The expression is TRUE if either input variable is TRUE

TRUE

1

FALSE

0

TRUE

1

TRUE

1

TRUE

1

FALSE

0

TRUE

1

FALSE

0

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Inclusive and Exclusive OR

Computers use inclusive ORStop the bus if passengerA OR

passengerB wants to get off Exclusive OR is different

You can get $1000 cash back or 0% financing

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Two Branches

Did you roll a doublet?die1 == die2 double moveNormal move

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Multiple Branches

What is your grade classification?>= 80 honours>= 60 passNot pass

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Looping

In Sequence and Branching, each action is performed at most once

Looping allows certain actions to be repeated

Keeps programs from getting large and unmanageable

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Example of Looping

Program specificationTake user inputs until they guess correctly

ProgramDeclare and initialize numberDeclare guess Input and compare guess Input and compare guess…

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Looping Icon

Loops have same components as branches

Condition selects one of two pathsOptional path “loops back” to condition

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Java syntax – branches

Basic shell

if (/*boolean expression*/)

{

// conditional statements

}

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Java syntax – exclusive branches

if (/*boolean expression*/)

{

// conditional statements

}

else

{

// default statements

}

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Java syntax – multiple branches

if (/*boolean expression*/){

// conditional statements} else if (/*boolean expression*/){

// more conditional statements}

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Java syntax – loops

Basic shell

while (/*boolean expression*/)

{

// repeatable statements

}

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Common Error

Decision to loop does not require a branch

Decisions are not structures Branches - selected actions Loops - repeated actions

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Sample Program – Telephone Banking

Write a program that implements an ATM interface1 – get balance2 – deposit3 – withdraw9 – end session

What are the key structures?