COM 111 LECTURE SCHEDULE 13

COM 111 LECTURE SCHEDULE 13

Generation of Programming Languages, Current Trends in Computer Programming and Languages

Programming and Languages.

INTRODUCTION:

Computers are machines. Unfortunately they cannot understand natural languages, such as Hindi, English, Tamil, etc. that human beings speak and understand.  Therefore, to give instructions to computers, different languages have been developed.  These languages are called computer languages.  To get a particular work done by computers, programmers write instructions using these computer languages.  Over the last few decades, several computer languages have developed.  Different computer languages are suitable for different applications.  For example, COBOL (Common business oriented Language) may be more suitable for business applications, FORTRAN may be more suitable for scientific or engineering applications. We can classify all computer languages into three categories. 

GENERATION OF PROGRAMMING LANGUAGES 

First Programmer  Lady Lovelace Ada Augusta (officially the first programmer) suggested binary numbers for computer storage instead of decimals.

1.First Generation : Machine Language

The form in which information is denoted or represented by a combination of “1” and “0”s is called machine language. Programs and data are ultimately represented in machine language in memory and other hardware of the computer. 

Advantages of Machine Language: 

v Translation Free:  Machine language is the only language that computers can directly execute without the need for conversion.

v High Speed:  Since no conversion is needed, the applications developed using machine language are extremely fast. 

Disadvantages of Machine Language: 

v Machine Dependent:   Every computer type differs from the other, based on its architecture.  Hence, an application developed for a particular type of computer may not run on the other type of computer.

v Complex Language:  Machine language is very difficult to read and write.  Since all the data and instructions must be converted to binary code, it is almost impossible to remember the instructions. 

v Error Prone:  Since the programmer has to remember all the opcodes and the memory locations, machine language is bound to be error prone.    

v Tedious:  Machine language poses real problems while modifying and correcting a program.   

2. Second Generation : ASSEMBLY LANGUAGE:  As computer field advanced, computer scientists felt the necessity of making computer programming easier. They invented computer languages that are easy to remember and use. These languages called assembly language uses mnemonic codes. for Example:  For adding two quantities X and Y, You may code as follows. 

ADD X Y ADD is called operation code that tells the computer what operation it has to perform. X and Y are called operation addresses. When the program is loaded into memory for execution the symbolic addresses are automatically converted into actual physical addresses of operands involved in an instruction. 

Assembler:

            The assembly language program must be translated into machine code by a separate program called an assembler. The assembler program recongnises the character strings that make up the symbolic names of the various machine operations, and substitutes the required machine code for each instruction.

Advantages of Assembly language:

v  Easy to Understand and use: The assembly language uses mnemonic codes, for programming. So it is easier for the programmer to use assembly language than machine language for programming.

v  Less Error Prone: The programmer does not have to keep track of the storage locations of the information and instructions. Hence , there are fewer errors while writing an assembly language program. Assemblers also provide various mechanisms to locate the errors.

v  Efficiency: Assembly programs can run much faster and use less memory and other resources than a similar program written in a high-level language. Speed increment of 2 to 20 times faster is common.

v  More control on Hardware: Assembly language also gives direct access to key machine features such as operating  system kernel or micro-kernel, device drivers and machine control.

Disadvantages of Assembly language:

v  Machine Dependent: Different computer architectures have their own machine and assembly languages, which means that programs written in these languages are not portable to other incompatible systems

v  Harder to Learn: Every type of computer architecture requires a different assembly language,  making it hard for a program to remember and understand every dialect of assembly.

v  Slow Development Time: Assembly generated applications are slower to develop as compared to high-level language based applications.

v  Less Efficient :  A program written in assembly language is less efficient as machine language because every assembly instruction has to be converted into machine language.

v  No Standardisation : Assembly languages cannot be standardised because each type of computer has a different instruction.

v  No support for Modern Software Engineering Technology: Assembly languages provide no inherent support for software engineering technology.

3. Third Generation : HIGH LEVEL LANGUAGES (3GL)

Due to computer’s widespread usage, early 1960s saw the emergence of the third generations programming languages (3GL).  Languages such as COBOL, FORTRAN, BASIC, and C are examples of 3GLs and are considered high-level languages.  

 In high-level language, programs are written in a sequence of statements to solve a problem.  For example, the following BASIC code snippet will calculate the sum of two numbers  

LET X  =  10 

LET  Y = 20 

LET  SUM  = X + Y  

PRINT SUM  

 Translating High-level Language to machine language:   

Since computers understand only machine language, it is necessary to convert the highlevel language programs into machine language codes.  This is achieved by using language translators or language processors, generally known as compliers, interpreters or other routines that accepts statements in one language and produces equivalent statements in another language. 

a) Compiler:   

     Compilers    Compiler is a program which translates source code written in a particular programming language into computer-readable machine code that can be directly loaded and executed.  For each high-level language, a separate compiler is required.  For example, a complier for C language cannot translate a program written in FORTRAN. 

A compiler is a kind of translator that translates a program into another program, known as target language.  The complier replaces single high-level statement with a series of machine language instruction.  Once the program has been compiled, the resulting machine code is saved in an executable file, which can be run on its own at any time. 

b) Interpreter: 

 Unlike compilers, an interpreter translates a statement in a program and executes the statement immediately, before translating the next source language statement.  When an error is encountered in the program, the execution of the program is halted and an error message is displayed.  Similar to compilers, every interpreted language such as BASIC and LISP has its own interpreters.

Advantages of High-Level Languages:  

v Readability:  Since high-level languages are closer to natural languages, they are easier to learn and understand. 

v Machine Independent:  program created using HLL can be used on different platforms with very little or no change at all.  

v Easy Debugging:  High-level languages include the support for ideas of abstraction so that programmers can concentrate on finding the solution to the problem rapidly

v Easier to Maintain:  The programs written in HLL are easy to modify and maintain because HLL programs are easier to understand.  

v Low Development Cost:  The cost of writing a HLL program is nearly constant for each line of code.  Thus, a high-level language, where each line of code translates to 10 machine instructions, costs only a fraction as compared to program developed in a low-level language. 

v Easy Documentation: Since the statements written in HLL are similar to natural languages they are easier to understand as compared to low-level languages.

Disadvantages of High-Level Languages:  

v Poor Control on Hardware:   High-level languages are developed to ease the pressure on programmers so that they do not have to know the intricacies of hardware

v Less Efficient:  The HLL applications are less efficient as far as computation time is concerned. 

4. Fourth Generation : (4GL)

• It is simple, English –like syntax rules, commonly used to access databases.
• 4GLs, on the other hand, are non-procedural languages
• The non-procedural methods is simple to state the needed output instead of specifying each step one after another to perform a task.
• The non-procedural methods is easier to write, but has less control over how each task is actually performed.
• 4GLs sacrifice computer efficiency in order to make programs easier to write.
• 4GL  have a minimum number of syntax rules.
• Common people can also use such languages to write application programs
• The 4GLs are divided into three categories.

1.    Query Languages:

They allow the user to retrieve information from databases by following simple syntax rules. For example to list only female employees .SQL and IBM’s Query – By- Example (QBE) are examples of query languages.

2.    Report Generators:

They produce customised reports using data stored in a database. The user specifies the data to be in the report. Making report generators very easy to use. 

3.    Application Generators:

The user writes programs to allow data to be entered into the database. The program prompts the user to enter the needed data.

Advantages of 4GLSs:

·                               A user can create an application in much shorter time for development and debugging.

·                               It does not require the programmers to provide the logic to perform a task.

·                               Lot of programming effort is saved.

·                               Use of procedural templates and data dictionaries allow automatic type checking.

·                               Using application generators, the routine tasks are automated.

Disadvantages of 4GLSs:

• Programs written in a 4GL are quite lengthy
• Need more disk space and a large memory capacity as compared to 3GLs
• These languages are inflexible
• These languages cannot directly utilise the computer power available at hardware level.

5. Fifth Generation : Very High-level Languages :

·      These languages will be able to process natural languages.

·      The computers would be able to accept, interpret and execute instructions in the native or natural language of the end uesrs.

·      The users will be free from learning any programming language to communicate with the computers.

·      The programmers may simply type the instruction or simply tell the computer by way of microphones.

Features of Good Programming Language:

• Ease of use
• Portability
• Reliability
• Safety
• Performance
• Cost
• Promote structural programming
• Maintainability
• Reusability
• Concurrency support
• Provides interface to other language
• Compact code