Chapter 15 Programming Languages

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Chapter 15 Programming Languages

• 15.1 Roles of a Programming Language 81
• 15.2 Development of Programming Languages 81
• 15.3 High-level Programming Languages 86
• 15.4 Translator 88

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15.1 The Roles of a Programming Language
Chapter 15 Programming Languages

• Programming Language
• Interface between machine and programmer
• Computer handles bits and bytes
• Has its own words and syntax
• Syntax
• is a set of rules that govern how the words are
  put together to form a Statement
• Programmers must obey syntax
• Algorithms
• ordered steps recorded on paper
• Programming
• realises algorithm

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15.2 Development of Programming Languages
Chapter 15 Programming Languages

• A. Low level Programming Language
• 1. First Generation Language
• 2. Second Generation Language
• B. High level Programming Language
• 1. Third Generation Language (3GL)
• 2. Fourth Generation Language (4GL)
• C. Comparison High Low Level languages

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15.2.1 Low-level programming languages
15.2 Development of Programming Languages

• Low-level programming languages
• include
• Machine languages and
• Assembly languages
• Machine dependent
• e.g. programs written in low-level languages for
  IBM PC cannot be run in a Macintosh computer
• Control hardware
• e.g. Driver programs are written in low-level
  languages.
• Programs written in low-level languages are
  usually
• small in size and
• efficient.

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15.2.1.1 First generation languages (1)
15.2 Development of Programming Languages

• The first generation programming languages
• Machine languages
• Defined by the hardware design of the computer
• Machine dependent.
• Instruction formed by binary digits (0or 1)
• Corresponding to an ON or OFF state of an
  electric circuit

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15.2.1.1 First generation languages (2)
15.2 Development of Programming Languages

• Machine Instruction has two parts
• op code operation to be performed
• a verb
• (e.g. increment, add, copy, etc)
• operand data to be acted on
• a noun
• (e.g. In incrementing the value of A, A is the
  operand)
• Operand may be a value or
• an address of memory location

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15.2.1.2 Second generation languages
15.2 Development of Programming Languages

• Second generation language
• Assembly languages
• Instructions are 11 with machine instructions
• Symbolic instruction code (or mnemonics)
• Using symbolic instruction code to replace binary
  digits.
• Meaningful abbreviations that substitute the op
  code
• e.g. JMP A means jump to address represented by
  A.
• Low-level languages
• Machine languages and assembly languages

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15.2.2 High-Level Programming Languages
15.2 Development of Programming Languages

• High-level languages
• Machine-independent
• Third generation languages or above
• More like human languages
• Let programmers concentrate on the logic
• Rather than machine architecture

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15.2.2.1 Third generation language (3GL)
15.2 Development of Programming Languages

• More human like than assembly language
• Meet demand of efficiency and effectiveness
• Examples
• C, Fortran, COBOL, BASIC, PASCAL etc.
• Each high-level language statement is translated
  into many machine instructions

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15.2.2.2 Fourth generation language (4GL)
15.2 Development of Programming Languages

• Each 4GL instruction represents many 3GL
  statements
• Typical example SQL (Structured Query Language)
• e.g.
• SELECT FROM student ORDER BY class,
  class_no
• will display all the records in table Student
  in ascending order of class and class_no.
• If the same task is written in a 3GL,
  instructions have to be written
• Sort the records in ascending order of class and
  class_no
• Get each record, test for end of file, put each
  item on screen
• Go back and repeat the operation until no more
  records to process

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15.2.3 Comparing Low High-level Languages (1)
15.2 Development of Programming Languages

• 1. Advantages of high-level language

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15.2.3 Comparing Low High-level Languages (2)
15.2 Development of Programming Languages

• 2. Advantages of low-level language

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15.3 Examples of High Level Languages (1)
Chapter 15 Programming Languages

• High Level Languages
• Designed to solve different problems
• Ranging from business to games
• Some common programming languages
• 1. PASCAL
• Designed for teaching structured programming
• Popular in schools

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15.3 Examples of High Level Languages (2)
Chapter 15 Programming Languages

• 2. C
• Designed to operate computer at low-level using
  high level language
• More readable and better structured than Assembly
  language
• 3. Java
• Includes some syntax of C
• Java programs can be called from HTML document or
  run directly
• Computer needs Java Virtual Machine to execute
  Java Programs

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15.3 Examples of High Level Languages (3)
Chapter 15 Programming Languages

• 4. COBOL
• Designed for business applications
• Wordy language
• Readable for beginners
• e.g.
• multiply hourly-rate by hours-worked
  giving gross-pay
• But, can be clumsy for long programs

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15.3 Examples of High Level Languages (4)
Chapter 15 Programming Languages

• 5. BASIC
• Designed to provide students with an
  easy-to-learn language.
• Visual Basic
• A version of BASIC
• Specialised for developing Windows applications
• Belong to Rapid Application Development (RAD)
• Programming can be done by drag-and-drop
• Programmers can quickly build an application
• Visual Basic.NET
• Newest version of Visual Basic
• Supports all Web-based features

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15.3 Examples of High Level Languages (5)
Chapter 15 Programming Languages

• 6. Script Languages
• Interpreted and processed by a software (e.g.
  Browser)
• Rather than a computer
• e.g.
• VBScript and JavaScript
• have similar syntax as Visual Basic and Java
  respectively
• Interpreted and processed by Web browser
• Instructions are embedded in HTML documents
• Increasing the function of HTML
• Making Web pages more interactive

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15.4 Translators (1)
Chapter 15 Programming Languages

• Source program
• Text file
• Storing source code
• Must be translated into machine instructions
  before execution
• Translator
• A software
• to convert source code into machine instructions
• Discover syntax errors of a program

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15.4 Translators (2)
Chapter 15 Programming Languages

• Object program
• Binary file
• Storing machine instructions
• During execution, needs the object program only
• A. Assembler
• B. Compiler
• C. Interpreter
• D. Trend in Translators
• E. Comparison of Translators

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15.4.1 Assemblers
15.4 Translators

• A. Assembler
• A software
• Translate assembly language program into machine
  instructions
• Producing one machine instruction for each
  assembly language statement
• Translate the whole source program before
  execution
• Storing the results in an object program
• During execution, need the object program only

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15.4.2 Compilers
15.4 Translators

• B. Compiler
• A software
• Translate high-level language program into
  machine instructions
• Translate the whole source program before
  execution
• Storing the results in an object program
• During execution, need the object program only

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15.4.3 Interpreters
15.4 Translators

• C. Interpreter
• A software for
• translating ONE high-level language program
  statement at a time
• send to the computer for execution
• then proceed to the NEXT statement
• No object program is produced
• When program is run, the following must be
  present
• interpreter and source code.
• Interpreted program runs slower than compiled
  ones
• Because time is spent on translation
• Like by programmers
• more convenient in testing

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15.4.4 Trend in translators
15.4 Translators

• Portability of programs
• The same program can be run on different OS
  without re-compilation
• Java
• Portable
• Source code of a Java program are not compiled
  into machine instructions
• But, compiled into intermediate code (bytecode)
• The object programs with bytecode are interpreted
  by an interpreter (called Java Virtual Machine,
  JVM)
• Users have to install JVM before use
• Microsofts Visual Studio.net use similar approach

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15.4.5 Comparison of Translators
15.4 Translators