TM105: Introduction to Computer
Programming
Meeting 1
Introduction to programs and Java
Objectives
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To understand algorithms.
To write a simple Java program.
To explain the basic syntax of a Java program.
To create, compile, and run Java programs.
To develop Java programs using IntelliJ.
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Programs
• You tell a computer what to do through programs.
• Without programs, a computer is an empty machine.
• Computer programs (software) are instructions to the
computer.
• Computers do not understand human languages, so you need
to use computer languages to communicate with them.
• Programs are written using programming languages.
• Good and logical programming is developed through good
pre-code planning and organization (Algorithm).
3
Programs
• An algorithm is an ordered set of unambiguous steps
that describes a process.
• An algorithm can be implemented in more than one
programming language.
• Algorithms can be designed though the use of
flowcharts or pseudocodes.
• Pseudocode uses English-like phrases to outline the
program.
• Flowchart is a graphical representation of an algorithm.
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Flowchart symbols
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Statement structures
• Sequence – follow instructions from one line to the
next without skipping over any lines
• Decision - if the answer to a question is “Yes” then
one group of instructions is executed. If the answer
is “No,” then another is executed
• Looping – a series of instructions are executed over
and over.
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The Sequence Structure
• The sequence structure is a case where the
steps in an algorithm are constructed in such a
way that, no condition step is required.
Example:
• Design an algorithm for finding the average of
six numbers, where the sum of the numbers is
given from the user.
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The Sequence Structure
Pseudocode
:
Flowchart
:
Start
Use variables: sum, average
Input sum
average = sum / 6
Output the average
Stop
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The Sequence Structure
Example:
Design an algorithm which will accept two
numbers from the user and calculate the sum
and the product, printing the answers on the
screen.
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The Sequence Structure
Pseudocode
:
Start
Use variables: sum, product, number1,
number2
Input number1, number2
sum = number1 + number2
print sum
product = number1 * number2
print product
Stop
Flowchart
:
Start
Input number1
Input number2
sum = number1 + number2
Print sum
product = number1 x
number2
Print
product
Stop
10
The Decision Structure
• The decision (selection) structure allows the program to make a
decision and change its behavior based on a condition.
• The condition is a logical test whose outcome is either true or false.
• The pseudocode and flowchart of the decision structure is shown
below.
• If the condition is true, Task-A is executed. If it is false, Task-B is
executed
Pseudocode
:
Flowchart
:
IF condition is true
task A
ELSE
task-B
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The Decision Structure
Example:
Design an algorithm of a program that reads from the user a
number and displays on the screen a message if this number
is positive or non-positive.
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The Decision Structure
Pseudocode
:Start
Flowchart
:
Use variable: number
Input number
IF number > 0
print (“Positive”)
ELSE
print (“Non-positive”)
Stop
Start
Input number
true
number > 0
Print (“Positive”)
false
Print (“Nonpositive”)
Stop
13
The Decision Structure
Example:
Design an algorithm of a program that reads from the user a
number representing the total score of a student and displays
on the screen a message if the student passed or failed.
A student passes, if the score is 50 or more. Otherwise, fails.
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The Decision Structure
Pseudocode
: Start
Use variable: score
Input score
IF score >= 50
print (“Pass”)
ELSE
print (“Fail”)
Stop
Flowchart
:
Start
Input score
true
score >= 50
Print (“Pass”)
false
Print (“Fail”)
Stop
15
Repetition
• Any program instruction that repeats some statement or sequence of
statements several times is called an iteration or a loop.
• The repetition structure can be done with the while loop.
• Loops are based on logical tests.
• The While loop: is used to repeat a statement or a block of statements
as long as a condition is true.
• The pseudocode syntax and flowchart of the while loop are:
Pseudocode
:
WHILE (condition)
A statement or block of statements
ENDWHILE
Flowchart
:
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Repetition
Example:
Design an algorithm for a program that prints the numbers
from 1 to 5.
Pseudocode:
Flowchart:
Use variable: number
number = 1
WHILE (number <= 5)
Print number
Add 1 to number
ENDWHILE
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Repetition
Example:
Write the pseudocode for reading the values of 6 test scores and finding their sum.
a) Pseudocode
1. Start
2. sum = 0
3. Get the 1st testscore
4. Add first testscore to sum
5. Get the 2nd testscore
6. Add to sum
7. Get the 3rd testscore
8. Add to sum
9. Get the 4th testscore
10. Add to sum
11. Get the 5th testscore
12. Add to sum
13. Get the 6th testscore
14. Add to sum
15. Output the sum
16. Stop
• Notice that there are repeated steps in
the solution.
• You should use loop.
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Repetition
The problem can be solved using loop:
Pseudocode:
Flowchart
Start
Use variables: testScore, sum, i
sum= 0
i=1
WHILE( i<=6)
Input testScore
sum = sum + testScore
i=i+1
ENDWHILE
Output sum
Stop
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Popular High-Level Languages
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Why Java?
• Java is one of the most used computer programming
languages in the world.
• Java is a general purpose programming language.
• Java is Object-Oriented (OO) — today’s key
programming methodology
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Interpreting/Compiling Source Code
• A program written in a high-level language is called a
source program or source code.
• Because a computer cannot understand a source code, a
source code must be translated into machine code for
execution.
• The translation can be done using another programming
tool called an interpreter or a compiler.
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Interpreting Source Code
• An interpreter reads one statement from the source
code, translates it to the machine code or virtual
machine code, and then executes it right away.
• A statement from the source code may be translated into
several machine instructions.
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Compiling Source Code
• A compiler translates the entire source code into
a machine-code file.
• The machine-code file is then executed.
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Java Programs
• To write Java programs, you need to download and install
the Standard Edition of Java Development Kit (JDK), which
is a development environment includes tools useful for
this purpose.
• You need also to download an Integrated Development
Environments (IDE) for Java. This is where you can edit and
run your Java code.
• IntelliJ is recommended since it is one of the most
powerful and popular IDEs.
• Guidelines for downloading IntelliJ are available on the
LMS.
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Java Programs
Java programs normally go through 3 steps:
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A Simple Java Program
Single-line comment
// This program prints Welcome to Java!
public class Welcome
{
public static void main(String[] args)
{
System.out.println("Welcome to Java!");
}
}
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A Simple Java Program
Multi-line comment
/* This program prints Welcome to Java!
Written by:……….
Date: ………… */
public class Welcome
{
public static void main(String[] args)
{
System.out.println("Welcome to Java!");
}
}
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Reserved words
• Reserved words or keywords are words that have a specific
meaning to the compiler and cannot be used for other purposes
in the program.
• Keywords are always spelled with all lowercase letters.
• public, class, static and void are all keywords.
!This program prints Welcome to Java//
{public class Welcome
{public static void main(String[] args)
;System.out.println("Welcome to Java!")
}
}
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Reserved words
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Class
• Every Java program must have at least one class.
• Each class has a name.
• Line 2 defines the class: Welcome
!This program prints Welcome to Java//
{public class Welcome
{public static void main(String[] args)
;System.out.println("Welcome to Java!")
}
}
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Class name
• Class name is a sequence of characters that
consists of letters, digits, underscores (_), and
dollar signs ($).
• A class name can not:
• Start with a digit.
• Be a reserved word.
• Contain space(s).
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Class name
Invalid class names:
Valid class names:
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Student
student
StudentClass
Student_class
Student$class$
Student1
_tudentClass$
$StudentClass
Class
Public
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123student
class
public
static
void
Student Class
1StudentClass
Student#Class
?StudentClass
It is good programming style to:
- choose meaningful and descriptive names for the class name.
- start the class name with an uppercase character.
The main Method
• Line 3 defines the main method.
• In order to run a class, the class must contain a method named
main.
• The program starts execution from the main method.
!This program prints Welcome to Java//
{public class Welcome
{public static void main(String[] args)
;System.out.println("Welcome to Java!")
}
}
34
Statements
• A statement represents an action or a sequence of actions.
• The statement System.out.println("Welcome to Java!") is a
statement to display (print) the message "Welcome to Java! ".
• "Welcome to Java! “ is a string.
• String simply is any sequence of characters enclosed between 2
double quotations "".
!This program prints Welcome to Java//
{public class Welcome
{public static void main(String[] args)
System.out.println("Welcome to Java!");
}
}
--output-Welcome to Java!
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Statements
• There are 3 different print methods in Java:
• print(): It prints its argument and does not add a new
line to the output.
• println(): It prints its argument and adds a new line to
the output.
• printf(): Is a formatted print (To e discussed later).
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Statement Terminator
Every statement in Java ends with a semicolon (;).
// This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
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Blocks
A pair of braces in a program forms a block that
groups components of a program.
Class
block
Method block
// This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
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Special Symbols
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Proper Indentation and Spacing
• Indentation
•
Indent some spaces to make your code neat and readable.
// This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args) {
System.out.println("Welcome to Java!");
}
}
• Spacing
•
Use blank line to separate segments of the code.
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Block Styles
There are 2 block styles for braces:
1. Next-line style:
// This program prints Welcome to Java!
public class Welcome
{
public static void main(String[] args)
{
System.out.println("Welcome to Java!");
}
}
2. End-of-line style:
// This program prints Welcome to Java!
public class Welcome {
public static void main(String[] args){
System.out.println("Welcome to Java!");
}
}
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What must you do before the next meeting?
• Read carefully the material of this meeting.
• Solve the exercises of the meeting.
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Exercises
Q1. Write Java programs to do the following:
1. Print your name and your student ID on the standard output in 2 lines.
2. Print the below text:
I
Love
Java
3. Print the first letter of your name on the standard output in a nice
format. For example, if your name is Ayman, you should print the letter
A as:
A
A
A
A
A
AAAAAAAAA
A
A
A
A
A
A
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Exercises
Q2. What is the exact output of the following pieces of code:
1.
System.out.print("Java is a ");
System.out.print("programming language");
2.
System.out.println("Java is a ");
System.out.print("programming language");
3.
System.out.println("Java is a\nprogramming\nlanguage");
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Exercises
Q3. The following code includes 10 compilation errors (an error per line):
1. Find and correct them.
2. Give the exact output after correcting the cod.
/ Try to find the errors
Public class Test1 {
public static main(String[] a) {
System.out.println('Welcome');
System.out.printIn("to");
System.out.println(“TM105);
System.out.print("Nice ")
System.out.println(Program);
{
]
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