Transcript CS102 Introduction to Computer Programming

CS102
Introduction to
Computer Programming
Week 1
Introduction and Chapter 1
Chapter 1
Intro to Programming and Program Design
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Why Program?
Computer Systems : Hardware and Software
Programs and Programming Languages
What is a Program Made of?
Input, Processing and Output
The Programming Process
Procedural and Object-Oriented Programming
Why Program?
• Computers perform a wide variety of tasks.
• Computer programmers provide the
software for computers.
• Software transforms a general purpose
computer into a specialized tool.
Concept - Computers can do many different jobs because
they are programmable.
What is Programming?
• Computers are designed to execute a set of
instructions.
• Programming is the act of creating a set of
instructions for a computer to execute.
• A set of instructions that performs a specific
task is called an algorithm.
Concept - A program is a set of instructions that a
computer follows in order to perform a task.
What a programmer does
• A programmer creates the following things:
– The logical flow of the instructions
– The mathematical procedures
– The appearance of the screens
• The way information is presented to the user
• The program's user friendliness
– Manuals and other forms of written
documentation
Concept – Make a general purpose machine perform a
specific task.
Computer Systems : Hardware
and Software
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Central Processing Unit
Main Memory
Input
Secondary Storage Device
Input Devices
Output Devices
Software :
– loaded from a secondary
storage device into main
memory
Computer
CPU
Output
Device
Main
Memory
Secondary
Storage
Central Processing Unit
The CPU consists of two parts
Control Unit
Performs three functions
• Fetch
• Decode
• Execute
Arithmetic & Logic Unit
Performs math operations
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Add
Shift
And
Or
Concept - The CPU is the heart of the computer.
Main Memory
• Referred to as:
– Random Access Memory (RAM)
• Static or dynamic
• Volatile
– Read Only Memory (ROM)
• Non-volatile
• Holds the program during execution
• Divided into equal sections called cells
– Each cell has a unique address
Secondary Storage
• Used to store programs and data for long
periods of time:
– Hard Drives
– Floppy
– Zip Drives
– Digital Tape
– CD ROMS
– Flash Memory Cards
• Categorized by speed and capacity
Input Devices
• Provide data to the CPU to be processed:
– Keyboards
– Touch sensitive screens
– Secondary storage devices
– Microphones
– Cameras
– Scanners
• Provide information in a variety of formats:
– Some conform to standards.
– Some are application unique.
Output Devices
• Displays or stores data for the user:
– Monitors
– Printers
– Speakers
– Disk Drives
– Modems
– Servers
• Consider the complexity of multimedia
output.
Software
• The instructions that tell the computer and
all of its devices what to do.
– When and what data to get
– What and how to manipulate the data
– When and how to provide it to the user
Concept – Software connects the user to the machine
Programming Languages
• Computers use machine language consisting
of numbers only.
• Humans have difficulty communicating
purely in numbers.
• A programming language provides a way for
humans to communicate with a computer
Concept - A program language is a special language used
to write computer instructions.
Some Popular Programming
Languages
BASIC
Beginners All-purpose Symbolic Instruction Code. A general programming
language originally designed to be simple enough for beginners to learn.
FORTRAN Formula Translator. A language designed for programming complex
mathematical algorithms.
COBOL
Common Business-Oriented Language. A language designed for business
applications.
Pascal
A structured, general purpose language designed primarily for teaching
programming.
C
A structured, general purpose language developed at Bell Labs. C offers
both high-level and low-level features.
C++
Based on the C language, C++ offers object-oriented features not found in
C. Also invented at Bell Laboratories.
Java
An object-oriented language invented at Sun Microsystems. Java may be
used to develop programs that run over the Internet, in a web browser.
The Importance of C++
• C++ is based on the C programming
language.
• C++ is a midlevel language containing
both high level and low level instructions.
• C++ is portable meaning that a C++
program can run a wide range of computers.
Concept - The popularity of C++ makes it an important
language to learn.
• Source Code
Code
Source Code
– Text written
by the programmer.
Pre-processor
• Modified Source code
Modified Source Code
– Expanded text produced
by the Pre-processor.
• Object Code
– Machine level code generated
by the compiler.
• Executable Code
– Machine level code generated
by the linker.
Compiler
Object Code
Linker
Executable Code
Language
Element
Key Words
What is a Program Made of?
Description
Words that have a special meaning. Key words may only
be used for their intended purpose.
Programmer Words or names defined by the programmer. They are
Defined
symbolic names that refer to variables or programming
Symbols
routines.
Operators Operators perform operations on one or more operands.
An operand is usually a piece of data, like a number.
Punctuation Punctuation characters mark the beginning or ending of a
statement, or separate items in a list.
Syntax
Rules followed when constructing a program. Syntax
dictates how key words and operators may be used, and
where punctuation symbols must appear.
Concept - There are certain elements common to all
computer programming languages.
Lines and Statements
• A line is one single line of program text
• A statement is:
– A complete instruction that causes the computer
to perform some action
– May consist of more than one line
• A C++ statement must end in a semicolon (;)
Concept - Programs are made of a complete statements.
Variables
• Symbolic names that represent locations in
the computer’s Random Access M
• Used to reference information that may
change throughout the execution of a
program
• The name of a variable should reflect the
purpose of the data it references
Concept - A program stores information in variables.
Variable Declarations
• Variables are either numbers or characters
• A variable declaration statement informs the
compiler:
– the name that will be assigned to the variable
– how it should be stored in memory
– it's initial value (optional)
• A variable definition statement causes a
variable to be created in memory.
Concept - Variables must be defined before they are used.
Input, Process, and Output
• A program takes data as input, processes it
and returns new data as output:
– Input usually comes from some external source
but can be the output of another process.
– Output is usually sent to an external device but
could be input to another process.
• A process determines the content of the
output.
Concept - The three primary activities of a program are input,
processing, and output.
The Programming Process
1. Clearly define what the program
is to do.
2. Visualize the program running
on the computer.
3. Design a flow or Hierarchy
chart.
4. Check the chart for logical
errors.
5. Write a pseudocode version of
the program.
6. Check the pseudocode for errors.
7. Write the actual program on
paper.
8. Desk check the program for
syntax or logical errors.
9. Enter the code and compile it.
10 . Correct any errors found
during compilation.
11. Run the test data for input .
12. Correct any logical errors
found while running the
program.
Concept - There are a number of steps involved in
successfully creating a program.
What is
Software Engineering?
Users
Needs
Analyze
Deliver
Maintain
Debug
Specify
Design
Code
Test
Modify
Document
Concept - Software engineering encompasses the whole
process of crafting computer software.
Procedural and Object-Oriented
Programming
• Procedural programming organizes code
into functional subroutines that perform
specific types of tasks.
• Object oriented programming addresses the
relationships between program features.
Concept - Procedural programming and object-oriented
programming are two ways of thinking about software
development and program design