Computer Fundamentals Chapter 12 cl

Computer Fundamentals: Pradeep K. Sinha & Priti Sinha

Ref Page Chapter 12: Computer Languages Slide 1/59


Learning Objectives

In this chapter you will learn about:
§ Computer languages or programming languages
§ Three broad categories of programming languages –
machine, assembly, and high-level languages
§ Commonly used programming language tools such as
assembler, compiler, linker, and interpreter
§ Concepts of object-oriented programming languages
§ Some popular programming languages such as
FORTRAN, COBOL, BASIC, Pascal, C, C++, C#, Java,
RPG, LISP and SNOBOL
§ Related concepts such as Subprogram, Characteristics of
a good programming language, and factors to consider
while selecting a language for coding an application

Ref Page 208 Chapter 12: Computer Languages Slide 2/59

Broad Classification of
Computer Languages

§ Machine language
§ Assembly language
§ High-level language



Machine Language

§ Only language of a computer understood by it
without using a translation program
§ Normally written as strings of binary 1s and 0s
§ Written using decimal digits if the circuitry of
the computer being used permits this


A Typical Machine Language
Instruction Format

OPCODE OPERAND
(operation code) (Address/Location)

§ OPCODE tells the computer which operation to perform
from the instruction set of the computer
§ OPERAND tells the address of the data on which the
operation is to be performed



A Sample Machine Language Program

001000000000001100111001 10001471
001100000000010000100001 14002041
011000000000011100101110 30003456
101000111111011100101110 50773456
000000000000000000000000 00000000

In Binary In Decimal
(Difficult to read and understand) (Easier to read and understand)



Advantages & Limitations of
Machine Language

Advantage

§ Can be executed very fast

Limitations

§ Machine Dependent
§ Difficult to program
§ Error prone
§ Difficult to modify



Assembly/Symbolic Language

Programming language that overcomes the limitations of machine
language programming by:

§ Using alphanumeric mnemonic codes instead of numeric codes for
the instructions in the instruction set
e.g. using ADD instead of 1110 (binary) or 14 (decimal) for
instruction to add
§ Allowing storage locations to be represented in form of alphanumeric
addresses instead of numeric addresses
e.g. representing memory locations 1000, 1001, and 1002 as FRST,
SCND, and ANSR respectively
§ Providing pseudo-instructions that are used for instructing the
system how we want the program to be assembled inside the
computer’s memory
e.g. START PROGRAM AT 0000; SET ASIDE AN ADRESS FOR FRST



Assembler

§ Software that translates as assembly language
program into an equivalent machine language program
of a computer

Assembly Input Output Machine
language language
Assembler program
program

One-to-one correspondence
(Source Program) (Object Program)


An Example of Assembly
Language Program

Mnemonic Opcode Meaning

HLT 00 Halt, used at the end of program to stop
CLA 10 Clear and add into A register
ADD 14 Add to the contents of A register
SUB 15 Subtract from the contents of A register
STA 30 Store A register

A subset of the set of instructions supported by a computer


Language Program

START PROGRAM AT 0000
START DATA AT 1000
SET ASIDE AN ADDRESS FOR FRST
SET ASIDE AN ADDRESS FOR SCND
SET ASIDE AN ADDRESS FOR ANSR
CLA FRST
ADD SCND
STA ANSR
HLT

Sample assembly language program for adding two numbers and
storing the result


Language Program

Symbolic name Memory location

FRST 1000
SCND 1001
ANSR 1002

Mapping table set up by the assembler for the data items
of the assembly language program


Language Program

Memory Contents Comments
location
Opcode Address
0000 10 1000 Clear and add the number stored at FRST to A register
0001 14 1001 Add the number stored at SCND to the contents of A
register
0002 30 1002 Store the contents of A register into ANSR
0003 00 Halt
-
-
-
1000 Reserved for FRST
1001 Reserved for SCND
1002 Reserved for ANSR

Equivalent machine language program for the assembly language program



Advantages of Assembly Language
Over Machine Language

§ Easier to understand and use
§ Easier to locate and correct errors
§ Easier to modify
§ No worry about addresses
§ Easily relocatable
§ Efficiency of machine language



Limitations of Assembly Language

§ Machine dependent
§ Knowledge of hardware required
§ Machine level coding



Typical Uses of Assembly Language

§ Mainly used today to fine-tune important parts of
programs written in a high-level language to improve
the program’s execution efficiency


Assembly Languages with
Macro Instructions

§ Any assembly language instruction that gets translated
into several machine language instructions is called a
macro instruction
§ Several assembly languages support such macro
instructions to speed up the coding process
§ Assemblers of such assembly languages are designed to
produce multiple machine language instructions for each
macro instruction of the assembly language



High-Level Languages

§ Machine independent
§ Do not require programmers to know anything about the
internal structure of computer on which high-level
language programs will be executed
§ Deal with high-level coding, enabling the programmers
to write instructions using English words and familiar
mathematical symbols and expressions



Compiler

§ Translator program (software) that translates a high-
level language program into its equivalent machine
language program
§ Compiles a set of machine language instructions for
every program instruction in a high-level language



Compiler

High-level Input Output Machine
language Compiler language
program program

One-to-many correspondence
(Source (Object
Program) Program)



Compiler

Program P1 in
Compiler for
high-level Machine code
language L1
language L1 for P1

Program P2 in Compiler for
high-level language L2 Machine code
language L2 for P2

A computer supporting languages L1 and L2

Illustrating the requirement of a separate compiler for each
high-level language supported by a computer

(Continued on next slide)



Compiler
(Continued from previous slide..)

Compiler for
language L1 Machine code for Executed on
on computer A P1 that will run computer A
on computer A

Program P1 in high-
level language L1 Same results
obtained

Compiler for Machine code for
language L1 Executed on
P1 that will run on
on computer B computer B
computer B

Illustrating the machine independence characteristic of a
high-level language. Separate compilers are required for the
same language on different computers



Syntax Errors

In addition to doing translation job, compilers also
automatically detect and indicate syntax errors

Syntax errors are typically of following types:

§ Illegal characters
§ Illegal combination of characters
§ Improper sequencing of instructions in a program
§ Use of undefined variable names

Note : A compiler cannot detect logic errors in a program



The Process of Removing Syntax Errors
From A Source Program
START

Edit
source program
Source program
Compile
source program

Syntax
errors No Generate
detected? object program

Yes Object program
Generate list of coded STOP
error messages



Linker

§ For a large software, storing all the lines of program
code in a single source file will be:

– Difficult to work with
– Difficult to deploy multiple programmers to
concurrently work towards its development
– Any change in the source program would require the
entire source program to be recompiled

§ Hence, a modular approach is generally adapted to
develop large software where the software consists of
multiple source program files
§ No need to write programs for some modules as it might
be available in library offering the same functionality



Linker

§ Each source program file can be independently
modified and compiled to create a corresponding
object program file
§ Linker program (software) is used to properly
combine all the object program files (modules)
§ Creates the final executable program (load module)



Interpreter

§ Interpreter is a high-level language translator
§ Takes one statement of a high-level language
program, translates it into machine language
instructions
§ Immediately executes the resulting machine language
instructions
§ Compiler simply translates the entire source program
into an object program and is not involved in its
execution



Role of an Interpreter

Interpreter
(translates and
High-level language executes
program Input Output Result of
statement-by-
(Source Program) program
statement)
execution


Intermediate Language Compiler &
Interpreter

§ New type of compiler and interpreter combines the
speed, ease, and control of both compiler and
interpreter
§ Compiler first compiles the source program to an
intermediate object program
§ Intermediate object program is not a machine
language code but written in an intermediate
language that is virtually machine independent
§ Interpreter takes intermediate object program,
converts it into machine language program and
executes it


Benefits of Intermediate Language
Compiler & Interpreter

§ Intermediate object program is in compiled form and thus is
not original source code, so safer and easier to share
§ Intermediate object program is based on a standard
Intermediate Definition Language (IDL)
§ Interpreter can be written for any computer architecture and
operating system providing virtual machine environment to the
executing program
§ Newer Interpreter compiles intermediate program, in memory,
into final host machine language program and executes it
§ This technique is called Just-In-Time (JIT) Compilation



Advantages of High-Level Languages

§ Machine independent
§ Easier to learn and use
§ Fewer errors during program development
§ Lower program preparation cost
§ Better documentation
§ Easier to maintain



Limitations of High-Level Languages

§ Lower execution efficiency
§ Less flexibility to control the computer’s CPU, memory
and registers



Object-Oriented Programming Languages

§ Programming languages are used for simulating real-
world problems on computers
§ Much of the real world is made up of objects
§ Essence of OOP is to solve a problem by:
§ Identifying the real-world objects of the problem
§ Identifying processing required of them
§ Creating simulations of objects, processes, and their
communications



FORTRAN

§ Stands for FORmula TRANslation
§ Originally developed by John Backus and his team at
IBM followed by several revisions
§ Standardized by ANSI as FORTRAN-77 and FORTRAN-90
§ Designed for solving scientific & engineering problems
§ Oriented towards solving problems of a mathematical
nature
§ Popular language amongst scientists and engineers



A Sample FORTRAN Program

C FORTRAN PROGRAM TO COMPUTE
C THE SUM OF 10 NUMBERS
SUM = 0
DO 50 I = 1, 10
READ (5, 10) N
SUM = SUM + N
50 CONTINUE
WRITE (6, 20) SUM
10 FORMAT (F6.2)
20 FORMAT (1X, ’THE SUM OF GIVEN NUMBERS = ’,
F10.2)
STOP
END



COBOL

§ Stands for COmmon Business Oriented Language
§ Originally developed started under Grace Hopper
followed by COnference on DAta SYstems Languages
(CODASYL)
§ Standardized by ANSI as COBOL-74, COBOL-85, and
COBOL-2002
§ Designed for programming business data processing
applications
§ Designed to have the appearance and structure of a
business report written in English, hence often referred
to as a self-documenting language



A Sample COBOL Program

IDENTIFICATION DIVISION.
PROGRAM_ID. SUMUP.
AUTHOR. P K SINHA.
* THIS PROGRAM COMPUTES AND PRINTS
* THE SUM OF GIVEN NUMBERS.

ENVIROMENT DIVISION.
CONFIGURATION SECTION.
SOURCE_COMPUTER. BURROUGHS_6700.
OBJECT_COMPUTER. BURROUGHS_6700.
INPUT_OUTPUT SECTION.
FILE_CONTROL.
SELECT DATA_FILE ASSIGN TO DISK.
SELECT OUTPUT_FILE ASSIGN TO PRINTER.

DATA DIVISION.
FILE SECTION.





FD DATA_FILE
RECORD CONTAINS 80 CHARACTERS
LABEL RECORD IS OMITTED
DATA RECORD IS INPUT_DATA_
RECORD.

01 INPUT_DATA_RECORD.
05 NPICTURE 9(6)V99.
05 FILLER PICTURE X(72).

FD OUTPUT_FILE
RECORD CONTAINS 132 CHARACTERS
LABEL RECORD IS OMITTED
DATA RECORD IS OUTPUT_RECORD.





01 OUTPUT_RECORD.
05 FILLER PICTURE X.
05TITLE PICTURE X(25).
05 SUM PICTURE 9(10)V99.
05 FILLER PICTURE X(94).
WORKING_STORAGE SECTION.
77MESSAGE PICTURE X(25)
VALUE IS “THE SUM OF GIVEN NUMBERS=”.

PROCEDURE DIVISION.
OPEN_FILES.
OPEN INPUT DATA_FILE.
OPEN OUTPUT OUTPUT_FILE.

INITIALIZATION.
MOVE SPACES TO OUTPUT_RECORD.
MOVE ZERO TO SUM.





PROCESS_LOOP.
READ DATA_FILE AT END GO TO
PRINT_PARA.
ADD N TO SUM.
GO TO PROCESS_LOOP.

PRINT_PARA.
MOVE MESSAGE TO TITLE.
WRITE OUTPUT_RECORD.

END_OF_JOB.
CLOSE DATA_FILE.
CLOSE OUTPUT_FILE.
STOP RUN.



BASIC

§ Stands for Beginners All-purpose Symbolic Instruction
Code
§ Developed by Professor John Kemeny and Thomas Kurtz
at Darmouth College in the United States
§ Standardized by ANSI as BASIC-78
§ Designed to be an interactive language and to use an
interpreter instead of a compiler
§ Simple to implement, learn and use language. Hence, it
is a widely used language on personal computers
§ Flexible and reasonably powerful language and can be
used for both business and scientific applications



A Sample BASIC Program

5 REM PROGRAM TO COMPUTE
6 REM THE SUM OF 10 NUMBERS
10 LET S = 0
20 FOR I = 1 TO 10
30 READ N
40 LET S = S + N
50 NEXT I
60 PRINT “THE SUM OF GIVEN NUMBERS = ”; S
70 DATA 4, 20, 15, 32, 48
80 DATA 12, 3, 9, 14, 44
90 END;



Pascal

§ Named after the famous seventeenth-century French
mathematician Blaise Pascal
§ Developed by Professor Nicklaus Wirth of Federal Institute of
Technology in Zurich
§ Encourages programmers to write well-structured, modular
programs, instills good program practices
§ Recognized as an educational language and is used to teach
programming to beginners
§ Suitable for both scientific & business applications
§ Has features to manipulate numbers, vectors, matrices,
strings, sets, records, files, and lists



A Sample Pascal Program
PROGRAM SUMNUMS (INPUT, OUTPUT);
(* PROGRAM TO COMPUTE THE SUM OF 10 NUMBERS *)

(* DECLARATION OF VARIABLES *)
VAR SUM, N : REAL;
VAR I : INTEGER;

(* MAIN PROGRAM LOGIC STARTS HERE *)
BEGIN
SUM := 0;
FOR I := 1 TO 10 DO
BEGIN
READ (N);
SUM := SUM + N;
END;
WRITELN (‘THE SUM OF GIVEN NUMBERS=’, SUM);
END;



C

§ Developed in 1972 at AT&T’s Bell laboratories, USA
by Dennis Ritchie and Brian Kernighan
§ Standardized by ANSI and ISO as C89, C90, C99
§ High-level programming languages (mainly machine
independence) with the efficiency of an assembly
language
§ Language of choice of programmers for portable
systems software and commercial software packages
like OS, compiler, spreadsheet, word processor, and
database management systems



A Sample C Program

/* PROGRAM TO COMPUTE THE SUM OF 10 NUMBERS */
/* Directives to include standard library and header */
#include <stdlib.h>
#include <stdio.h>
/* Main function starts here */
void main ( )
{
/* Declaration of variables */
float Sum = 0.0, N = 0.0;
int Count = 0;
for (Count = 0; Count < 10; Count++)
{
printf(“nGive a number:”);
scanf(“%f”, N);
Sum += N;
}
printf(“THE SUM OF GIVEN NUMBERS = %f”, &Sum);
}



C++

§ Named C++ as ++ is increment operator and C
language is incremented to its next level with C++
§ Developed by Bjarne Stroustrup at Bell Labs in the
early 1980s
§ Contains all elements of the basic C language
§ Expanded to include numerous object-oriented
programming features
§ Provides a collection of predefined classes, along with
the capability of user-defined classes



Java

§ Development started at Sun Microsystems in 1991 by a
team led by James Gosling
§ Developed to be similar to C++ with fewer features to
keep it simple and easy to use
§ Compiled code is machine-independent and developed
programs are simple to implement and use
§ Uses just-in-time compilation
§ Used in embedded systems such as hand-held devices,
telephones and VCRs
§ Comes in two variants – Java Runtime Engine (JRE) and
Java Software Development Kit (SDK)



C# (C Sharp)

§ Object-oriented programming language developed by
Anders Hejlsberg and released by Microsoft as part of
Microsoft’s .NET technology initiative
§ Standardized by ECMA and ISO
§ Syntactically and semantically very close to C++ and
adopts various object-oriented features from both C++
and Java
§ Compilers target the Common Language Infrastructure
(CLI) implemented by Common Language Runtime (CLR)
of .NET Framework
§ CLR provides important services such as, memory
management, exception handling, and security



RPG

§ Stands for Report Program Generator
§ Developed by IBM to meet customer requests for an
easy and economic mechanism for producing reports
§ Designed to generate the output reports resulting from
the processing of common business applications
§ Easier to learn and use as compared to COBOL
§ Programmers use very detailed coding sheets to write
specifications about input, calculations, and output



LISP

§ Stands for LISt Processing
§ Developed in 1959 by John McCarthy of MIT
§ Designed to have features for manipulating non-
numeric data, such as symbols and strings of text
§ Due to its powerful list processing capability, it is
extensively used in the areas of pattern recognition,
artificial intelligence, and for simulation of games
§ Functional programming language in which all
computation is accomplished by applying functions to
arguments



SNOBOL

§ Stands for StriNg Oriented symBOlic Language
§ Used for non-numeric applications
§ Powerful string manipulation features
§ Widely used for applications in the area of text
processing


Characteristics of a Good
Programming Language

§ Simplicity
§ Naturalness
§ Abstraction
§ Efficiency
§ Structured Programming Support
§ Compactness
§ Locality
§ Extensibility
§ Suitability to its environment



Factors for Selecting a Language for
Coding an Application

§ Nature of the application
§ Familiarity with the language
§ Ease of learning the language
§ Availability of program development tools
§ Execution efficiency
§ Features of a good programming language



Subprogram

§ Program written in a manner that it can be brought into
use in other programs and used whenever needed
without rewriting
§ Also referred to as subroutine, sub-procedure, or function
§ Subprogram call statement contains the name of the
subprogram followed by a list of parameters enclosed
within a pair of parentheses
§ Intrinsic subprograms (also called built-in-functions) are
those provided with the programming language
§ Programmer-written subprograms are written and used
as and when they are needed



Structure of a Subprogram

Subprogram name Parameter

Subprogram header
sqrt (x)

Set of instructions that perform Subprogram body
the intended task



Flow of Control in Case of Subprogram Calls

subprogram header 2 1
subprogram call statement
3
6 4 next statement
subprogram body 7
5

subprogram call statement
8 next statement
9

A subprogram Flow of control A program that calls
the subprogram twice



Key Words/Phrases

§ Assembler § Just-in-time compilation
§ Assembly language § Language processor
§ BASIC § Linker
§ Built-in function § LISP
§ C § Load module
§ C++ § Logic error
§ C# § Low-level language
§ COBOL § Machine language
§ Coding § Macro instructions
§ Compiler § Object program
§ Computer language § Object-oriented programming
§ FORTRAN § Opcode
§ Function § Operand
§ High-level language § Pascal
§ HotJava Interpreter § Programmer
§ Intrinsic subprogram § Programming
§ Intermediate compiler and § Programming language
Interpreter § Pseudo instruction
§ Java § RPG
§ Self-documenting language




Key Words/Phrases

§ SNOBOL
§ Source program
§ Sub-procedure
§ Subprogram
§ Subroutine
§ Symbolic language
§ Syntax error
§ Syntax rules
§ Written subprograms


Computer Fundamentals Chapter 12 cl

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Computer Fundamentals Chapter 12 cl