This document provides an overview of computer programs and programming. It discusses what a computer program is, how programs interact with hardware, the planning and writing of code, and different types of programming languages. Key points include: - Computer programs contain instructions that the CPU executes to perform tasks. There are different types like operating systems, utilities, and applications. - Programs are stored in files with various extensions like .exe, .dll, and .ini. Code instructs the CPU to perform actions like playing a sound. - Programming languages simplify writing code by using English-like syntax. Examples of languages mentioned are C++, Java, Visual Basic, and Perl. - There are lower-level languages close to

1. Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill Technology Education
McGraw-Hill Technology Education Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.

2. Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.McGraw-Hill Technology Education
Chapter 13A
Creating Computer
Programs

3. 13A-3
What Is a Computer Program?
• Computer programs
– Also called software
– Computer programs are the list of
instructions. Instructions are called code
– CPU execute the instructions
– Three types of computer programs
• Operating system
• Utility
• Application

4. 13A-4
Software Is Stored In Many Files
• Executable files
– Contain the instructions for the CPU
– Have extensions of .exe
• Many other extensions are commonly found
.dll extension
.ini extension
.hlp extension

5. 13A-5
Hardware/Software Interaction
• Program execution
– Software executes at the CPU level
– Code to play a sound
• Code generates an interrupt
• CPU tells the sound card to play
• Sound card plays the file
– Programmer creates the code

6. 13A-6
Hardware/Software Interaction
• Code
– Statements written in a programming
language
– Writing code can be tedious
• Code must be perfect
• Order of steps must be exact
– Writing code is quite exciting
• Problems are solved
• New ideas are formed

7. 13A-7
Writing Code

8. 13A-8
Hardware/Software Interaction
• Machine code
– Recall that computers think in binary
– Code is translated into machine code
• CPU executes the machine code
– CPUs have a unique machine code

9. 13A-9
Hardware/Software Interaction
• Compilers and interpreters
– Converts source code into binary
• Allows code to execute
– Checks source code for correctness

10. 13A-10
Hardware/Software Interaction
• Compiler
– Creates an executable file
• Contents are called object code
– Executable can run on its own
– Each language has its own compiler
– C++ and Java are compiled languages

11. 13A-11
Hardware/Software Interaction
• Interpreter
– Runs program one line at a time
– More flexible than compilers
– Slower than compilers
– Always needed to execute program
– Visual Basic and Perl are interpreted

12. 13A-12
Planning a Computer Program
• Plans
– The steps to solve a problem
– Describe the expected results
– Programming without a plan is difficult

13. 13A-13
Planning Tools
• Pseudo code
– Natural language statements that
resemble code
– Describes what must be done
– Can be written by non programmers
– Programmers develop unique versions

14. 13A-14
How Programs Solve Problems
• Program control flow
– Order program statements are executed
– Typically executed in order
– Constructs can change the flow
• Decision statements
• Loops

15. 13A-15
How Programs Solve Problems
• Algorithm
– Set of steps
– Always leads to a solution
– Steps are always the same
– Flowcharts can describe algorithms
• Structured tool for drawing algorithms
– Algorithms appear in all programs

16. 13A-16
Hardware/Software Interaction
• Programming languages
– Simplifies the writing of code
• English is used to describe the binary
– Original code is called source code
– Several hundred languages exist

17. PROGRAMING LANGUAGES
13A-17

18. 13A-18

19. Low Level Language
• A low-level language is a programming
language is very close to writing actual
machine instructions.
• Low-level languages are considered more
difficult to use, however, because they require
a deeper knowledge of the computer's inner
workings.
• Two good examples of low-level languages
are assembly and machine code.
13A-19

20. 1. Machine language
• Programming language that can be directly
understood and obeyed by a machine
(computer) without conversion.
• It is different for each type of CPU
• it is the native binary language (comprised
of only characters: 0 and 1) of the computer
and is difficult to be read and understood by
humans
• Hardware dependent: Could be performed
by only one type of computer with a
particular CPU.
13A-20

21. 2. Assembly Language
• An assembly language is a low-level
programming language for microprocessors
and other programmable devices.
• Assembly language implements a symbolic
representation of the machine code needed to
program a given CPU architecture.
• It is not just a single language, but rather a
group of languages.
• Examples: x86
13A-21

22. Higher level Language
• High-level language is any programming language
that enables development of a program in much
simpler programming context and is generally
independent of the computer's hardware
architecture.
• High-level language has a higher level of abstraction
from the computer, and focuses more on the
programming logic rather than the underlying
hardware components such as memory addressing
and register utilization.
• C/C++ and Java are popular examples of high-level
languages.
13A-22

23. Procedural Languages
• Procedural programming language is
a list or set of instructions telling a
computer what to do step by step and
how to perform from the first code to the
second code.
• Procedural programming languages
include C, Go, Fortran, Pascal, and
BASIC.
13A-23

24. Non-Procedural Languages
– A computer language that does not require
writing traditional programming logic.
– Also known as a "declarative language,"
users concentrate on defining the input
and output rather than the program steps
required in a procedural programming
language
– Many are associated with specific
application packages.
• Query Languages:
• Report Writers:
• Application Generators:13A-24

25. Object-oriented programming (OOP)
• It is a programming language model
organized around objects rather than
"actions" and data.
• Historically, a program has been
viewed as a logical procedure that takes
input data, processes it, and produces
output data.
• Examples: C++/JAVA, Smalltalk
13A-25