1. ICT1412 - Introduction to Programming
Chapter 1 – Program Design

2. What is Programming? Programming is applied problem-solving
Understand a problem
Identify relevant characteristics
Design an algorithm (step-by-step sequence of instructions to carry out a task)
Implement the algorithm as a computer program
Test the program by repeated (and carefully planned) executions
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
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3. Understanding the Programming Process
The programmer’s job can be broken down into six programming steps as follows:
Understand the problem
Plan the logic
Code the program
Translate the program into machine language
Test the program
Put the program into production
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4. 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
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5. 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
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6. 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
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7. 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
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8. 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
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9. Creating an Executable Program
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10. 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
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11. 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
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12. 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
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13. 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
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14. 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
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15. 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
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16. 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
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17. Using Flowchart Symbols and Pseudocode Statements (Cont.)
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18. Using Flowchart Symbols and Pseudocode Statements (Cont.)
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
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19. 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
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20. 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
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21. 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:
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22. 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
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23. Six Basic Computer Operations
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
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
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24. Six Basic Computer Operations (Cont.)
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
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25. Six Basic Computer Operations (Cont.)
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:
To give data an initial value in pseudocode, the verbs Initialize or Set are used
To assign a value as a result of some processing the symbols '=' is written e.g. GPA = sum/count
To keep a variable for later use, the verbs Save or Store are used
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26. Six Basic Computer Operations (Cont.)
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
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27. Six Basic Computer Operations (Cont.)
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
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28. Pseudocode for Decimal Addition
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29. 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 ...
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30. 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
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31. 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
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32. 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:
Must be one word
Have some appropriate meaning
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33. 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
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34. 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
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35. 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
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36. 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
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37. Algorithm Characteristics
Those characteristics were:
Ordered set of instructions
Effective instructions
Unambiguous instructions
Terminates
There are other concerns for algorithms besides those characteristics
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38. 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?
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39. 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
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40. 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
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41. 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
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42. 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
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43. 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
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44. 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++)
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45. 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!
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46. Regular Programming Languages
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47. Java
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48. 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)
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49. 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
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50. 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)
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51. 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
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52. Java Program Structure (Cont.)
// comments about the class
public class MyProgram { }
class header
class body
Comments can be placed almost anywhere
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53. Java Program Structure (Cont.)
// comments about the class
public class MyProgram { }
// comments about the method
public static void main (String[] args) { }
method header
method body
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54. 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 */
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55. 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-Code
Ask user to enter a diameter, D, or enter zero to stop
Repeat until D=0
Set circumference to pi * D
Set area to pi * (D/2)2
Output circumference and area
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56.      double circumference, area;
Ask user to enter a diameter, D, or enter zero to stop
Repeat until D=0
Set circumference to pi * D
Set area to pi * (D/2)2
Output circumference and area    
double circumference, area;
//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 ”);
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
Last, and definitely least, add the mumbo-jumbo that goes around every Java program …
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57. To get started with Java, type in this program and run it…
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…
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58. 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)
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59. 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
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60. Software Development Tools
Using Sun Java SDK alone
Programmer
Command Line Interface
Source
File(s)
(.java)
Compiler
(javac)
Class
(.class)
Virtual
Machine
(java)
Editor
Program
executes
Parts of Sun Java SDK
bytecode
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61. Software Development Tools (Cont.)
We will use a combination of the JCreator LE IDE and the Sun Java SDK (both of them are freeware!)
Source
File(s)
(.java)
Programmer
JCreator LE
Compiler
(javac)
Class
(.class)
Virtual
Machine
(java)
Edit
Build
Run
Program
executes
Parts of Sun Java SDK
Graphical User Interface
bytecode
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62. Types of Programming Errors
A program can have three types of errors:
The IDE editor and/or compiler will find syntax errors and other basic problems (compile-time errors)
A problem can occur during program execution, such as trying to divide by zero, which causes a program to terminate abnormally (run-time errors)
A program may run, but produce incorrect results, perhaps using an incorrect formula (logical errors)
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63. 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
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64. 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.java
creates the file HelloWorld.class (assuming, of course, there are no syntax errors!)
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