Download Intro-comp

University of Hail
College of Computer Science & Engineering
Computer Science and Software Engineering Department
ICS 102
Computer Programming
ICS 102
Computer Programming
Chapter1 : Introduction
Components of a Personal Computer
Questions :
- what are the input devices ?
- what are the output devices ?
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Motherboard
A motherboard, provides the electrical
connections by which the other components
of the system communicate and hosts the
central processing unit as well as other
subsystems and devices .
4
Motherboard example : Acer E360
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CPU (Central Processing Unit)
The Central Processing Unit (CPU) or
processor is the portion of a computer system
that carries out the instructions of a computer
program and is the primary element carrying
out the computer's functions.
Example: (3 + 2) = 5
In an addition operation, the arithmetic
logic unit (ALU) will be connected to a
set of inputs and a set of outputs. The
inputs provide the numbers to be added,
and the outputs will contain the final
sum .
3
5
2
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Memory
 Memory refers to computer components, devices, and recording
media that hold digital data used for computing for some interval of
time.
 There are mainly three types of memory :

CPU memory
◦ Registers
◦ Cache

Main memory (RAM):
◦ Data has to be in main memory so that CPU can access it
◦ Volatile: lost when program exits; computer shuts off

Hard Disk, CD, etc.
◦ This is where you keep the data for long-term storage
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Main Memory …
Address
1002
1003
1004
1005
Cell
Memory is divided into
Many memory locations (cells)
Each memory cell has a
numeric address, which
uniquely identifies it
Each cell contains a data
value, e.g. 22
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Main Memory …
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Main Memory …
The word “Hello.” stored in 6 memory cells
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Memory units : Bits and Bytes

Bit -- most basic unit of memory
◦ 1 or 0, on or off

1 Byte = 8 bits

In a computer, data values are stored as a sequence of bits
1004
2
1004
00000010
1005
7
1005
00000111
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Program / CPU / Memory Interaction

Example:
◦ Input read a number from keyboard
◦ Add 1 to it
◦ Output it on screen
Keyboard
1
RAM
1
1
CPU
2
RAM
2
2
Monitor
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Software
 Software
is the programs and data that
a computer uses.
Both programs and data are saved in
computer memory in the same way.
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Computer Software
Types of software
Software
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Software
Application Programs
Systems Programs
Word processors
Game programs
Spreadsheets
Data base systems
Graphics programs
Web browsers
Operating system.
Networking system.
Programming
language software.
Web site server.
Device drivers.
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What is programming?
What is a program?

A (software) program is a list of instructions
intended to a computer

A program has inputs and outputs

Each instruction tells the computer to do
something (an action, a calculation, a
comparison)
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Program Execution

A program tells the CPU how to manipulate and/or
move information

Programming is about processing information
◦ Take some input,
◦ manipulate it in some way, and
◦ produce a particular output
Program
Inputs
Manipulation
Outputs
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Example 1 : Recipe for Scrambled Eggs

Ingredients (Inputs) : two eggs,
tablespoon of oil, salt

Instructions (program):
◦ Add oil to pan
◦ Heat pan on stove
◦ Crack eggs into pan
◦ Add salt
◦ Mix until light and flakey

Output: scrambled eggs
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Example 2 : Currency Exchange
Task : convert an amount of money in some currency (e.g. US
Dollars) to another one (e.g. Saudi Riyals).
Input:
◦ Amount
◦ Source Currency
◦ Desired Currency
 Instructions
◦ Look up in table current exchange rate for the
selected currencies
◦ Calculate result as amount * exchange rate
• Output: result

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Programming language

A programming language is the language used to
write programs

A programming language employs a set of rules
that dictate how the words and symbols can be
put together to form valid program statements

A programming language has a syntax and
semantics

In this course we focus on Java programming
language.
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Java
• Java is a programming language originally
developed by James Gosling at Sun
Microsystems
• It was first released in 1995.
• The language derives much of its syntax
from C and C++.
• But has a simpler object model and fewer
low-level facilities than C and C++.
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Programming Language Hierarchy
High-Level Language (HLL)
Assembly Lanuage
Machine Language
Hardware
The highs and lows of programming
languages ...

High-Level Language (HLL)  Machine Language
◦ closest to natural language (lowest level)
◦ words, numbers, and math
◦ natural language for
symbols
hardware
◦ not directly understood
◦ just 0s and 1s
by hardware
◦ directly understood
◦ Java, C/C++, COBOL,
by hardware
FORTRAN, BASIC, Lisp,
Ada, etc.
Assembly Language (middle level)
a more or less human readable version of
machine language
 words, abbreviations, letters and numbers
 easily translated from human readable to
machine executable code

Getting from Source to Machine Code

“Compiler”
a program that translates HLL source code to machine
(object, or executable) code.

“Assembler”
a program that translates assembly source code to machine
(object, or executable) code.
Compilers vs. Assemblers vs. Interpreters

Compilers and Assemblers
◦ translation is a separate user step
◦ translation is “off-line,” i.e. not at run time

Interpreters
◦ interpretation (from source to object code) is not a separate
user step
◦ translation is “on-line,” i.e. at run time
Source
Code
Compiler,
Assembler, or
Interpreter
Object
Code
Java Program Translation
Data for Java Program
Java Program

Intermediate Code:
“Byte Code”
◦ similar to assembly code,
but hardware independent

Interpreter translates from
generic byte code to
hardware-specific machine
code
Java Compiler
Byte-Code
Program
Java
Virtual
Machine
Byte-Code Interpreter
Machine-Language
Instructions
Computer Execution
of Machine-Language Instructions
Output of Java Program
Byte-Code and the Java Virtual Machine

The Java compiler translates Java programs into
byte-code, a machine language called the Java Virtual
Machine
◦ Once compiled to byte-code, a Java program can be used
on any computer, making it very portable
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Portability of Java
Classical model :
Java model :
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Program terminology

Code: A program or a part of a program

Source code (or source program): A program written
in a high-level language such as Java
◦ The input to the compiler program

Object code: The translated low-level program
◦ The output from the compiler program, e.g., Java bytecode
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Portability of Java
Write once, run anywhere :Because applications written in
the Java programming language are compiled into machineindependent bytecodes, they run consistently on any Java
platform .
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A Java Program
A Java Program

A Java program consists of
one or more classes

A Java class consists of one or
more methods

A Java method consists of one
or more statements
Java
classes
Java
Methods
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A Java Program

A Java program resides in one or more files.

The file name of a Java program has extension .java.

One of the classes of a Java program is called the driver
class.

The name of the driver class must be the same as the name
of its Java file. (Java is case sensitive. So EX1 is different from
ex1.)

The driver class must contain a method called main. The
execution of Java program starts from the main method of
the driver class.
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Example of a Java Program
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Example of a Java Program
Class name
Main method
Class body
Instruction
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Example of a Java Program
Also notice:
Curly braces { }
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Example of a Java Program
Also notice:
Curly braces { }
Parentheses ( )
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Example of a Java Program
Also notice:
Curly braces { }
Square brackets [ ]
Parentheses ( )
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Example of a Java Program
Also notice:
A pair of braces { }
define a block
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Compiling and running a program

Type in your program

Save the program
◦ Store all your files in one directory for now
◦ Give the program the same name as the class

Compile the program
◦ this produces a .class file
◦ Translates the program into something the computer can
understand and execute (Java bytecode)

Run the program

Observe the result and adjust the program if necessary
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Edit
Public class firstPtog
/*
This program is an …
*/
Public class
/*
Text Editor
public static void main…
/* Program statements g …
System.out.print(“Wel …
}
}
firstProg.java
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Compile - With Errors
Public class firstPtog
/*
This program is an Arit
*/
public static void main
/* Program statements g
System.print(“Welcome
}
Compiler
}
firstProg.java
Errors and Warnings
------------------Error : The method print(
String) is undefined for
Type System
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Compile - Success
Public class firstPtog
/*
This program is an Arit
*/
public static void main
/* Program statements
System.out.print(“Welcome”);
}
Compiler
}
firstProg.java
001011010001011101
1011010001011101110
101000101110111010110100010
111011101011010001011101110
101101000101110111010110100
010111011100010111011101011
010001011101110010111011101
011010001011101110010111011
101011010001011101110010111
011101011010001011101110010
111011101011010001011101110
0101110
firstPtog.class
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Run Program
Fred
1
firstProg
Welcome to the Arithm
The date is Monday Sep
What is your name?Fred
Well Fred, after a day
The cube appears to be
You find a Green door,
The door closes behind
There is a feel of mat
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