Chapter 4 computer language

Contents
• Machine language programming
• Programming process
• Programming languages
• Levels of programming languages
• Program translator

Learning Objectives
• At the end of this chapter, students should
be able to:
– Identify and utilize the programming
processes.
– Identify the different levels of programming
languages.
– Identify and differentiate the program
translators.

Machine Language Programming
• What is programming language?
– A language for instructing computer
• What is source code?
– A complete program in such language
• What is machine language?
– The most primitive type of programming
language that computer understands
(instruction can be executed by the CPU)

• Earliest form of programming
• Most tedious and time consuming since it
requires programmers to:
– determine the exact set of primitive machine
actions (instructions) necessary to perform
complex task
– write down each instruction in an
understandable form to the computer

• Computer’s instruction set are defined by the set
of data manipulation and movement functions of
which the CPU is capable to perform.
• The processing functions of a typical CPU can
be classified into 3 categories:
– Computation – perform mathematical calculation
using two numbers as input and store the result
– Comparison – compare the values of two stored
numbers and determine if they are equivalent
– Data movement – move an individual item of data
from one storage location to another storage location

High Level Language Program
Machine Language Code
Micro Steps (Micro Code)
Memory Bus System ALU etc.
HW
Decoder
Control Signal
Language Processing
Translation from SW to HW

Programming Process
• What is programming Language?
– A set of rules that provide a way of telling a
computer what operations to perform.
• What is program?
– Set of step-by-step instructions that direct the
computer to do the task users want it to do
and produce the results.

Programming Process
• Programming process includes:
– define the problems
– plan the solution
• through developing an algorithm that includes the
flowchart and pseudo-code
– coding the program
– test the program
– document the program

Programming Process
• Defining a problem:
– Programmer meets users of the client
organization or system analyst will analyze
the problems.
– Written agreement is produced.
– Items of input, process and output are being
identified.

Programming Process
• Planning the solution
– Most common way of planning is by having
flow charts or write pseudo-code
– Flowchart is a pictorial diagram of an ordered
step by step solution to a problem

Programming Process
Process
Decision
Connector
Start or Stop Program
Input or Output
Direction of Flow
ANSI Standard Flow Chart Symbols

Programming Process
Example of simple flow
chart – of what to do if a
lamp doesn’t work

Programming Process
• Planning the solution
– Pseudo-code is an English-like language that
states the solution with more precision in
English but less precision than is required
when using a formal language.
– Example:
if credit card number is valid
execute transaction based on number and order
else
show a generic failure message
end if

Programming Process
• Coding the programs
– The programmer translate the logic from the flow
chart or pseudo-code to a programming language or
source code
– The programmer has to know the syntax and the
format of writing the programming

Programming Process
• Testing the program
– Involve the desk-checking, the translating, and the
debugging phases.
• Desk-checking involves a programmer sitting down to
proof-read a program.
• Translating involves a translator – using compiler or
interpreter (a program that translates the instruction into a
form the computer can understand).
• Debugging involves detecting, locating, and correcting bug
or mistakes or errors by running the program.

Programming Process
• Documenting the program
– Is necessary and is an ongoing process.
– Documentation is a written detail descriptions of the
programming cycle and specific facts about the
program.
– Typical program documentation materials include:
• The origin and the nature of the problem.
• A brief narrative description of the program.
• Logic tools such as flowcharts, pseudo-codes and/or flow
charts.
• Data record descriptions
• Program listings and testing results.

Programming Languages
• Programming languages are said to be lower
(closer to the computer) or higher (closer to
people/users).
• There are five generations of programming
languages to be enlisted from the lowest to the
highest levels, which are:
– Machine language.
– Assembly language.
– High-level language (HLL).
– Very high-level language (VHLL).
– Natural language.

Higher
Lower
Machine
Users

• Machine language
– The lowest level of language
– Represents data as 1s and 0s (binary digits
corresponding to the “on” and “off” electrical
states (switching actions) in a computer.

• Assembly language
– Uses mnemonic codes
– Mnemonic codes are abbreviations that are easy to
remember and to replace the machine language
numbers
– Even though not in English words, they are still
convenient and are preferable than numbers alone.
– Uses an assembler program to turn its program into
a machine language.
– Has disadvantages such as vary by machine,
extremely detail, making programming becomes
repetitive, tedious and prone to making errors.

• High-level Language (HLL)
– More English-like – thus making it more
convenient
– FORTRAN (FORmula TRANslator) is the 1st
HLL
– Other examples of HLL are COBOL, BASIC,
ALGOL, APL, FORTH, LISP, LOGO, Modula-
2, PILOT, PLI, PROLOG and RPG.

• Very high-level language (VHLL)
– Known as a 4th generation language (4GL)
– Usually nonprocedural (user need to write only
“what” is to be done but not “how”.
– A procedural language tells the computer how a task
is done (a very specific step-by-step process)
– Advantages - increase productivity, require minimal
training and allow users to be unconcern about the
HW or program structure.

• Natural language
– Is named because of its resemblance to spoken
English.
– Referred to as knowledge-based language due to
its usage in interacting with a base of knowledge on
some subject, resulting in a knowledge-based
system (KBS), such as an expert system.
– Natural language excel at easy data access
– This has evolved into a language namely structured
query language (SQL).

• Object-oriented programming (OOP)
– A group of languages : called object-oriented
language (OOL) group.
– OOL is based on a more active, visual programming
environment.
– Structured languages treat data and tasks
(instructions) separately.
– OOL views data and tasks together for each object
(entity that may be grouped in classes and contains
its own code).
– Current examples OOP languages are Object Logo,
JAVA, C++, Turbo Pascal, and SmallTalk.

• Hybrid object-based programming
languages
– Are visual in a manner similar to OOP language but
lack certain features.
– The 1st hybrid language : HyperCard (Macintosh)
– Some object-based hybrids are classified as visual
programming languages because they are
distinguished by the ability to build programs
connecting links between various objects.
– Current examples of visual programming languages
are Object Vision and Visual Basic (VB).

Program Translator
• What is program translator?
– A program that transform/translate source
code into machine readable code.
• There are 3 types of program translator:
– Assembler
– Compiler
– Interpreter

Program Translator
• Assembler
– A program that translates the instruction
(assembly language code) into a form that
computer can understand (machine language
code).
MOV AX, 0005
ADD AX, 0010
ADD AX, 002
MOV [0120], AX
INT 20
Assembler
Output File
1011100000000101000000
0000000101000100000000
0000000001010010000000
0000001010001100100000
Symbolic
program
Binary
program

Program Translator
ADD AX, 0010 05 10,00
Opcode in
Assembly
Language
Operand1
Operand2
Opcode in
Machine
Language
Operand1
Operand2
Notes that:
ADD translated into
05 AX translated into
000010 translated into
1016
Assembly Language
Machine Language (Binary) Machine Language
(Hexadecimal)
MOV AX,0005 10111000 00000101 00000000 B8 05 00
ADD AX,0010 00000101 00010000 00000000 05 10 00
ADD AX,0020 00000101 00100000 00000000 05 20 00
MOV [0120],AX 10100011 00100000 00000001 A3 20 01
INT 20 11001101 00100000 CD 20

Program Translator
• Compiler
– A compiler translates a program in a
programming language
– The original program is called the source
code
– The result of translating source code is called
the object code

Program Translator
• Compiler
– How a compiler compile a program?
• Source code is read from a file by the compiler and
object code is written to a newly created file
• The source code file is named to indicate the
programming language, such as program.java
where “.java” indicates a JAVA program
• Object code filenames generally have an “.o” or
“.obj” appended to original root filename, such as
program.o or program.obj.

Program Translator
• Compiler
– Source code statements are read into the
compiler one at a time
– 3 classes of source code statements are:
• Data declaration
• Data operation
• Control structure

Program Translator
• Compiler:
– Data declaration:
• Set memory locations to store the declared data.
• The amount of memory allocated depends on the
type of the data, such as integer, real, character
etc.
• The compiler builds an internal table, known as
symbol table to keep track of the data names,
types and assigned memory addresses.

Program Translator
• Compiler
– Data operation
• As data operations are encountered in source
code, they are translated into the sequence of
machine instructions necessary to implement
those operations.
• These instruction sequences include primitive data
manipulation instructions as well as any necessary
data movement instructions.

Program Translator
• Compiler
– Control structure
• Example of control structure includes
unconditional branches (such as GOTO
statement or subroutine call), conditional
branches (such as IF-THEN-ELSE statement),
and loops (such as WHILE-DO, FOR and
REPEAT-UNTIL statement).

Program Translator
• Compiler
– Support Libraries
• The object code consists entirely of executable
machine instructions and data such as executable
code.
• Certain types of language statements, including
data declarations, control structures are converted
into executable codes (external subroutines).
• These external subroutines can be found in either
one of these places:
– Compiler library
– Library call

Program Translator
• Compiler
– Linking
• Note that, the preceding library call is not a CPU instruction.
• Library call is a reference to a set of executable code that
has been previously compiled and stored in a library for later
use.
• Therefore, it must be replaced by the corresponding library
code before application can be executed.
• A program called a linker or link editor performs this
replacement.
• The process of replacement is called linking, link editing or
binding.

Program Translator
• Interpreter
– While compilation process is in progress, link editing
and program execution cannot occur until the entire
source code file has been compiled
– In contrast, interpretation interleaves source code
translation and execution
– An interpreter reads a single statement of the source
code, translates into machine instruction, and
immediately executed
– One program (the interpreter) translates and executes
another (the source code) one statement at a time

Chapter 4 computer language

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Chapter 4 computer language