ICT1412 - Introduction to Programming Chapter 1 – Program Design.

ICT1412 - Introduction to Programming

Chapter 1 – Program Design

Prepared by K.T. Ng 2

What is Programming? Programming is applied problem-solving1. Understand a problem2. Identify relevant characteristics3. Design an algorithm (step-by-step sequence of

instructions to carry out a task)4. Implement the algorithm as a computer program5. Test the program by repeated (and carefully

planned) executions6. GO BACK AND REPEAT AS NECESSARY In short: programming is the process of

designing, writing, testing and debugging algorithms that can be carried out by a computer


Understanding the Programming Process

The programmer’s job can be broken down into six programming steps as follows:

1. Understand the problem2. Plan the logic3. Code the program4. Translate the program into machine

language5. Test the program6. Put the program into production


1. Understand the Problem

Really understanding the problem may be one of the most difficult aspects of programming The description of what the user needs may

be vague The user may not even really know what he

or she wants Users who think they know what they want

frequently change their minds after seeing sample output


2. Plan the Logic

Programmer plans the steps to the program, deciding what steps to include and how to order them

The two most common tools are flowcharts and pseudocode

Both tools involve writing the steps of the program in English


3. Code the Problem

Some very experienced programmers can successfully combine the logic planning and the actual instruction writing, or coding of the program, in one step

A good final project report needs planning before writing, and so do most programs


4. Translate the Program into Machine Language

Languages such as Java or C translate the programmer’s English-like high-level programming language into the low-level machine language that the computer understands

If you write a programming language statement incorrectly (for example, by misspelling a word, using a word that doesn’t exist in the language, or using “illegal” grammar), the translator program doesn’t know what to do and issues an error message identifying a syntax error


4. Translate the Program into Machine Language (Cont.)

All syntax errors are caught by the compiler or interpreter

When writing a program, a programmer might need to recompile the code several times

An executable program is created only when the code is free of syntax errors

When you run an executable program, it might also typically require input data


Creating an Executable Program


5. Test the Program

A program that is free of syntax errors is not necessarily free of logical errors

Once a program is free from syntax errors, the programmer can test it — that is, execute it with some sample data to see whether the results are logically correct


6. Put the Program into Production

Putting a program into production might mean simply running the program once, if it was written to satisfy a user’s request for a special list

The process might take months if the program will be run on a regular basis, or it is one of a large system of programs being developed

Conversion, the entire set of actions an organization must take to switch over to using a new program or set of programs, can sometimes take months or years to accomplish


Algorithms The central concept underlying all computation

is that of the algorithm An algorithm is a step-by-step sequence of

instructions for carrying out some task Programming can be viewed as the process of

designing and implementing algorithms that a computer can carry out

A programmer’s job is to: Create an algorithm for accomplishing a given

objective, then Translate the individual steps of the algorithm into a

programming language that the computer can understand


Algorithms in the Real World The use of algorithms is not limited to

the domain of computing e.g., recipes for baking cookies e.g., directions to your house

In order for an algorithm to be effective, it must be stated in a manner that its intended executor can understand

a recipe written for a master chef will look different than a recipe written for a college student

As you have already experienced, computers are more demanding with regard to algorithm specifics than any human could be


Representing Algorithms

What language to use? Natural language (e.g. English).

Does not provide the accuracy and precision needed to represent an algorithm.

Formal programming languages (e.g. C++, Java). At this level we don’t think at the abstract level More concerned with punctuation, grammar, and syntax

Pseudocode Does not matter how you choose to write the

instructions: set, store, etc Not a precise set of notation rules to be memorized and

rigidly followed


Using Flowchart Symbols and Pseudocode Statements

Flowcharts (pictorial representations) and pseudocode (English-like representations) are used by programmers to plan the logical steps for solving a programming problem

Some professional programmers prefer writing pseudocode to drawing flowcharts, because using pseudocode is more similar to writing final statements in programming language


Using Flowchart Symbols and Pseudocode Statements (Cont.)

Almost every program involves the steps of input, processing, and output, necessitating some graphical way to separate them

Arithmetic operation statements are examples of processing in a flowchart, where you use a rectangle as the processing symbol containing a processing statement

To represent an output statement, you use the parallelogram, which is also the same symbol used for input statements





In flowcharts: Arrows, or flowlines, connect and show the

appropriate sequence of steps A terminal symbol, or start/stop symbol,

should be included at each end Often, “start” or “begin” is used as the first

terminal symbol and “end” or “stop” is used in the other


Using Flowchart Symbols and Pseudocode Statements (Cont.) Figure below shows a complete flowchart for

the program that doubles a number, and the pseudocode for the same problem


Using the Connector By using just the input, processing, output,

decision, and terminal symbols, you can represent the flowcharting logic for many diverse applications

When drawing a flowchart segment, you might use only one other symbol, the connector

You can use a connector when limited page size forces you to continue a flowchart in an unconnected location or on another page

By convention, programmers use a circle as an on-page connector symbol, and a symbol that looks like a square with a pointed bottom as an off-page connector symbol


Using the Connector (Cont.) If a flowchart has six processing steps and a

page provides room for only three, you might represent the logic as shown below:


How to Write Pseudocode

When designing a solution algorithm, you need to keep in mind that a computer will eventually perform the set of instructions written

If you use words and phrases in the pseudocode which are in line with basic computer operations, the translation from pseudocode algorithm to a specific programming language becomes quite simple


Six Basic Computer Operations

1. A computer can receive information When a computer is required to receive information

or input from a particular source, whether it is a terminal, a disk or any other device, the verbs Read and Get are used in pseudocode

2. A computer can put out information When a computer is required to supply information

or output to a device, the verbs Print, Write, Put, Output, or Display are used in pseudocode

Usually an output Prompt instruction is required before an input Get instruction


Six Basic Computer Operations (Cont.)

3. A computer can perform arithmetic Most programs require the computer to perform some

sort of mathematical calculation, or formula, and for these, a programmer may use either actual mathematical symbols or the words for those symbols

To be consistent with high-level programming languages, the following symbols can be written in pseudocode:

+ for Add - for Subtract* for Multiply / for Divide ( ) for Parentheses

When writing mathematical calculations for the computer, standard mathematical ‘order of operations’ applies to pseudocode and most computer languages



4. A computer can assign a value to a variable or memory location

There are three cases where you may write pseudocode to assign a value to a variable or memory location:

1. To give data an initial value in pseudocode, the verbs Initialize or Set are used

2. To assign a value as a result of some processing the symbols '=' is written e.g. GPA = sum/count

3. To keep a variable for later use, the verbs Save or Store are used



5. A computer can compare two variables and select one or two alternate actions

An important computer operation available to the programmer is the ability to compare two variables and then, as a result of the comparison, select one of two alternate actions

To represent this operation in pseudocode, special keywords are used: if, if … else



6. A computer can repeat a group of actions When there is a sequence of processing steps

that need to be repeated, special keywords for leading decision loops (do…while), trailing decision loops (repeat…until) and counted loops (do), are used in pseudocode

The condition for the repetition of a group of actions is established in the do...while clause, and the actions to be repeated are listed beneath it


Pseudocode for Decimal Addition


What Operations Do We Need?

Getting input and producing output Get the two numbers Display the outcome

Referring to values within our algorithm Add together the rightmost digits of the two numbers Add together a0 and b0

Doing something if some condition is true If the outcome is greater or equal to 10 then ...

Doing something repeatedly Do this for all the digits in the numbers ...


Pseudocode Primitives

The Structure Theorem states that it is possible to write any computer program by using only three basic control structures that are easily represented in pseudocode: Sequence Selection Repetition


The Three Basic Control Structures

Sequence The sequence control structure is the straightforward

execution of one processing step after another In pseudocode, we represent this construct as a

sequence of pseudocode statements Selection

The selection control structure is the presentation of a condition and the choice between two actions; the choice depends on whether the condition is true or false

In pseudocode, selection is represented by the keywords if; if … else


Using and Naming Variables Variables are memory locations, whose

contents can vary or differ over time For instance, in our previous doubles a number

example, inputNumber can hold a 2 and calculatedAnswer will hold a 4; at other times, inputNumber can hold a 6 and calculatedAnswer will hold a 12

A variable name is also called an identifier Variable names used here follow only two

rules:1. Must be one word2. Have some appropriate meaning


Ending a Program By Using Sentinel Values

An infinite loop is a repeating flow of logic with no end

To end the program, set a predetermined value for inputNumber that means “Stop the program!”

The program can then test any incoming value for inputNumber and, if it is a 0, stop the program

Testing a value is also called making a decision Represented in flowchart by diamond shape called a

decision symbol


Ending a Program By Using Sentinel Values (Cont.)

A pre-selected value that stops the execution of a program is often called a dummy value since it does not represent real data, but just a signal to stop

Sometimes, such a value is called a sentinel value because it represents an entry or exit point, like a sentinel who guards a fortress


Understanding Data Types Computers deal with two basic types of data —

character and numeric When you use a specific numeric value, such

as 43, within a program, you write it using the digits and no quotation marks

A specific numeric value is often called a numeric constant because it does not change — a 43 always has the value 43

When you use a specific character value, or string of characters, such as "Chris" you enclose the string, or character constant, within quotation marks


Understanding Data Types (Cont.)

Some languages allow for several types of numeric data

Languages such as Pascal, C++, C#, and Java distinguish between integer (whole number) numeric variables and floating-point (fractional) numeric variables containing a decimal point


Algorithm Characteristics

Those characteristics were: Ordered set of instructions Effective instructions Unambiguous instructions Terminates

There are other concerns for algorithms besides those characteristics


Algorithm Characteristics (Cont.)

Efficiency: This can be a very important concern for algorithms. Two key types: Time efficiency Space efficiency

Correctness: Of course, this tends to be the most important concern! If the algorithm is not correct, and does not

do the task it was intended for, what good is it?


From Pseudo-Code to Java

Once satisfied with an algorithm, the programmer translates the algorithm into a program The algorithm was written in pseudo-code The program is to be written in a

programming language of some kind In our case, we are particularly

interested in translating algorithms into Java


From Pseudo-Code to Java (Cont.)

To do this, one needs to know how each algorithmic construct: data storage/retrieval data manipulation sequential execution conditional execution repetition

is represented in Java; that is: Java syntax We will be seeing these in more detail

later


Understanding the Evolution of Programming Techniques

Old programming languages required programmers to work with memory addresses and to memorize awkward codes associated with machine languages

Newer programming languages look much more like natural language and are easier to use


Understanding the Evolution of Programming Techniques (Cont.)

Currently, there are two major techniques used to develop programs and their procedures Procedural programming focuses on the

procedures that programmers create Object-oriented programming, focuses

on objects, or “things”, and describes their features, or attributes, and their behaviors


Java Java is based upon C++ (which in turn is

based on C) Unlike C++ which is really a hybrid language,

Java is purely Object-Oriented This results in significant advantages Most HLL (High Level Language) programs are

compiled to run on a single platform Java programs can run on multiple platforms

after compilation --- i.e. its compiled format is platform independent

Java and C++ are the dominant languages in industry


History of Java Java was developed by J. Gosling at Sun

Microsystems in 1991 for programming home appliances (variety of hardware platforms)

With the advent of the WWW (1994), Java’s potential for making web pages more interesting and useful was recognized. Java began to be added to web pages (as applets) that could run on any computer (where the browser was running)

Since then it has been more widely accepted and used as a general-purpose programming language, partly due to

its platform-independence, and it is a truly OO language (unlike C++)


Platform-Independence Notion of a “Java Virtual Machine” (JVM) Java programs are compiled to run on a virtual

machine (just a specification of a machine). This code is called Byte Code

Each physical machine that runs a Java program (byte code) must “pretend” to be a JVM

This is achieved by running a program on the machine that implements the JVM and interprets the byte code to the appropriate machine code

This interpreting is done at run-time which can cause a slow down!


Regular Programming Languages


Java


Object-Oriented Programming

The OOP paradigm uses the notion of objects and classes as basic building blocks

Other important components of OOP are Encapsulation (next semester) Inheritance (next semester) Polymorphism (next semester)


Classes and Objects Object-oriented programs use objects An object represents a concept that is part of our

algorithm, such as an Account, Vehicle, or Employee

Similar objects share characteristics and behavior. We first define these common characteristics for a group of similar objects as a class

A class defines the type of data that is associated with each object of the class, and also the behavior of each object (methods)

A class is a template for the objects An object is called an instance of a class Most programs will have multiple classes and

objects


Banking Example In a banking application, there may be numerous accounts There is common behavior (as far as the bank is concerned)

for all these accounts Deposit Check balance Withdraw Overdraw?

There are also common types of data that the bank in interested in

Account holder’s name(s), HKID, … Current balance, recent transactions, …

Instead of defining these data and behavior for each account separately, we simple define them once --- this is the notion of the account class

Each account will be an instance of this class and will have its own values for the data items, but the same behavior (defined once)


Java Program Structure

In the Java programming language: A program is made up of one or more classes

A class contains one or more methods A method contains program statements

These terms will be explored in detail throughout the course

A Java application always contains a method called main


Java Program Structure (Cont.)

public class MyProgram

{

}

// comments about the class

class header

class body

Comments can be placed almost anywhere


Java Program Structure (Cont.)

public class MyProgram

{

}

// comments about the class

public static void main (String[] args)

{

}

// comments about the method

method headermethod body


Comments Comments in a program are called inline

documentation They should be included to explain the purpose

of the program and describe processing steps They do not affect how a program works Java comments can take three forms:// this comment runs to the end of the line

/* this comment runs to the terminating symbol, even across line breaks */

/** this is a javadoc comment */


An Example from Pseudo-Code to Java

Write a program that computes the circumference and area of circles given their diameter

Step 1 write Pseudo-CodeAsk user to enter a diameter, D, or enter zero to stopRepeat until D=0 Set circumference to pi * D Set area to pi * (D/2)2

Output circumference and area Ask user to enter a diameter, D, or enter zero to stop


//Compute and print the circumference of circles, //given their diameter as input from the userdouble D = Console.readInt(“Please enter a diameter, or enter zero to stop ”);while (D>0) //user doesn’t want to stop{

circumference = 3.14 * D;area = 3.14 * (D/2) * (D/2); //pi * radius2

System.out.println(“the circumference is ” + circumference + “ and the area is ” + area);

D = Console.readInt(“Please enter a diameter, or enter zero to stop ”);} //end of while loop

Ask user to enter a diameter, D, or enter zero to stopRepeat until D=0

Set circumference to pi * DSet area to pi * (D/2)2

Output circumference and areaAsk user to enter a diameter, D, or enter zero to stop

double circumference, area;

Last, and definitely least, add the mumbo-jumbo that goes around every Java program …


public class Circles{ public static void main(String[] args) { //Compute and print the circumference of circles, //given their diameter as input from the user double D = Console.readInt(“Please enter a diameter, or enter zero to stop ”); double circumference, area; while (D>0) //user doesn’t want to stop {

circumference = 3.14 * D;area = 3.14 * (D/2) * (D/2); //pi * radius2

System.out.println(“the circumference is ” + circumference + “ and the area is ” + area);

D = Console.readInt(“Please enter a diameter, or enter zero to stop ”); } //end of while loop }}

To get started with Java, type in this program and run it…


Software Development Tools

Software Development Tools or Kits (SDK’s) are specialized application programs that allow programmers to write and test programs

Experienced programmers generally prefer an “Integrated Development Environment” (IDE)

Examples (that we’ll be using in this course): Sun’s Java SDK (sometimes called JDK) JCreator LE (Version 4.0)


Styles of User Interface

There are two predominant styles of User Interface for any type of program: Command Line Interface (CLI) Graphical User Interface (GUI)

As a computer programmer, you must be able to use and write programs for both styles of user interface


Software Development Tools Using Sun Java SDK alone

Programmer

Command Line Interface

SourceFile(s)(.java)

Compiler(javac)

ClassFile(s)(.class)

VirtualMachine

(java)

Editor

Programexecutes

Parts of Sun Java SDK

bytecode


Software Development Tools (Cont.)

We will use a combination of the JCreator LE IDE and the Sun Java SDK (both of them are freeware!)

SourceFile(s)(.java)

Programmer

JCreator LE

Compiler(javac)

ClassFile(s)(.class)

VirtualMachine

(java)

Edit Build Run

Programexecutes

Parts of Sun Java SDK

Graphical User Interface

bytecode


Types of Programming Errors

A program can have three types of errors:

1. The IDE editor and/or compiler will find syntax errors and other basic problems (compile-time errors)

2. A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors)

3. A program may run, but produce incorrect results, perhaps using an incorrect formula (logical errors)


Compiler Errors and Warnings An executable program will not be generated by

the compiler if compile-time errors exist in your program

View the error messages, and deal with them one at a time, starting with the first error

When a compiler reports Warnings you should take note of them

Warnings alone will not prevent the generation of an executable program, but they do point to possible problems

You should ALWAYS aim for 0 warnings and 0 errors


More On Java Programming More details about Java programming:

Regarding file names: Each Java program has a name A program must be stored in a file named with the

program name and the extension .java e.g. program name: HelloWorld

file: HelloWorld.java contains the Java code Regarding compiling the source code:

The compiler creates the bytecode version of the code and stores it in a file with the extension .class

e.g. javac HelloWorld.javacreates the file HelloWorld.class (assuming, of course, there are no syntax errors!)

Date post:	27-Dec-2015
Category:	Documents
Upload:	stewart-osborne
View:	235 times
Download:	1 times

ICT1412 - Introduction to Programming Chapter 1 – Program Design.

Documents