Levels of programming languages

18/11/2021

Levels of programming languages

Low level language
1. machine
2. assembly
High Level languages
1. third Generation Languages (3GLs)
2. four Generation Languages (4 GLs)
3. Object Oriented Programming (OOPs)
4. Internet (scripting) Programming Languages

LEVELS OF PROGRAMMING LANGUAGES

There are many programming languages. The languages are classified into 2 major categories:

Low-level programming languages.
High-level programming languages.

Each programming language has its own grammatical (syntax) rules, which must be obeyed in order to write valid programs, just as a natural language has its own rules for forming sentences.

LOW-LEVEL LANGUAGES

These are the basic programming languages, which can easily be understood by the computer directly, or which require little effort to be translated into computer understandable form.
They include:

Machine languages.
Assembly languages.

Features of low-level languages

They are machine hardware-oriented.
They are not portable, i.e., a program written for one computer cannot be installed and used on another computer of a different family.
They use Mnemonic codes.
They frequently use symbolic addresses.

Machine languages (1st Generation languages)

Machine language is written using machine codes (binary digits) that consist of 0’s & 1’s.

The computer can readily understand Machine code (language) instructions without any translation.

A programmer is required to write his program in strings of 0’s & 1’s, calculate & allocate the core memory locations for his data and/or instructions.

Different CPU’s have different machine codes, e.g., codes written for the Intel Pentium processors may differ from those written for Motorola or Cyrix processors. Therefore, before interpreting the meaning of a particular code, a programmer must know for which CPU the program was written.

A machine code instruction is made up of 2 main parts;

An Address (operand):
It specifies the location (address) of the computer memory where the data to be worked upon can be found.
A Function (operation) code:
It states to the Control Unit of the CPU what operation should be performed on the data/item held in the address, e.g., Addition, Subtraction, Division, Multiplication, etc.

Note. The computer can only execute instructions which are written in machine language. This is because; it is the only language which the computer can understand. Therefore, any program written in any other programming language must first be translated into machine language (binary digits) before the computer can understand.

Assembly language (2nd Generation Languages).

Assembly languages were developed in order to speed up programming (i.e., to overcome the difficulties of understanding and using machine languages).

The vocabulary of Assembly languages is close to that of machine language, and their instructions are symbolic representations of the machine language instructions.

Assembly language programs are easier to understand, use & modify compared to Machine language programs.
Assembly language programs have less error chances.

To write program statements in Assembly language, the programmer uses a set of symbolic operation codes called Mnemonic codes.

The code could be a 2 or 3 shortened letter word that will cause the computer to perform specific operation. E.g., MOV – move, ADD - addition, SUB – subtraction, RD - read.

Example;
RD PAT, 15 (read the value 15 stored in the processor register named PAT)
SUB PAT, 10 (subtract 10 from the value in register PAT)

A program written in an Assembly language cannot be executed/obeyed by the computer hardware directly. To enable the CPU understand Assembly language instructions, an Assembler (which is stored in a ROM) is used to convert them into Machine language.

The Assembler accepts the source codes written in an Assembly language as its input, and translates them into their corresponding computer language (machine code/ object code) equivalent.

Comments are incorporated into the program statements to make them easier to be understood by the human programmers.

Assembly languages are machine-dependent. Therefore, a program written in the Assembly language for a particular computer cannot run on another make of computer.

Advantages of Low-level languages

The CPU can easily understand machine language without translation.
The program instructions can be executed by the hardware (processor) much faster. This is because; complex instructions are already broken down into smaller simpler ones.
Low-level languages have a closer control over the hardware, are highly efficient & allow direct control of each operation.
They are therefore suitable for writing Operating system software & Game programs, which require fast & efficient use of the CPU time.
They require less memory space.
Low-level languages are stable, i.e., they do not crash once written.

Disadvantages of Low-level languages

Very few computer programs are actually written in machine or Assembly language because of the following reasons;

Low-level languages are difficult to learn, understand, and write programs in them.
Low-level language programs are difficult to debug (remove errors from).
Low-level languages have a collection of very detailed & complex instructions that control the internal circuiting of the computer. Therefore, it requires one to understand how the computer codes internally.
Relating the program & the problem structures is difficult, and therefore cumbersome to work with.
The programs are very long; hence, writing a program in a low-level language is usually tedious & time consuming.
The programs are difficult to develop, maintain, and are also prone to errors (i.e., it requires highly trained experts to develop and maintain the programs).
Low level languages are machine-dependent (specific), hence non-portable.
This implies that, they are designed for a specific machine & specific processor, and therefore, cannot be transferred between machines with different hardware or software specifications.
It is not easy to revise the program, because this will mean re-writing the program again.

HIGH-LEVEL PROGRAMMING LANGUAGES

High-level languages were developed to solve (overcome) the problems encountered in low-level programming languages.

The grammar of High-level languages is very close to the vocabulary of the natural languages used by human beings. Hence; they can be read and understood easily even by people who are not experts in programming.

Most high-level languages are general-purpose & problem-oriented. They allow the programmer to concentrate on the functional details of a program rather than the details of the hardware on which the program will run.

High-level language programs are machine-independent, (i.e., they do not depend on a particular machine, and are able to run in any family of computers provided the relevant translator software is installed).

Programs written in a high-level language cannot be obeyed by the computer hardware directly. Therefore, the source codes must be translated into their corresponding machine language equivalent. The translation process is carried out by a high-level language software translator such as a Compiler or an Interpreter.

Features of high-level programming languages.

They contain statements that have an extensive vocabulary of words, symbols, sentences & mathematical expressions, which are very similar to the normal English language.
Example;
Read (TaxablePay);
IF TaxablePay<1000 THEN
Tax: =0;
ELSE
Tax: =TaxRate * TaxablePay;
Write (Tax: 6:2);
Allow modularization (sub-routines).
They are ‘user-friendly’ and problem-oriented rather than machine-based. This implies that, during a programming session, the programmer concentrates on problem-solving rather than how a machine operates.
They require one to be obey a set of rules when writing the program.
Programs written in high-level languages are shorter than their low-level language equivalents, since one statement translates into several machine code instructions.
The programs are portable between different computers.

Purpose of High-level languages.

To improve the productivity of a programmer. This is because; the source programs of high-level languages are shorter than the source programs of low-level languages, since one statement translates into several machine code instructions.
To ease the training of new programmers, since there is no need to learn the detailed layout of a procession/sequence.
To speed up testing & error correction.
To make programs easy to understand & follow.

Advantages of High-level languages.

They are easily portable, i.e., they can be transferred between computers of different families and run with little or no modification.
High-level language programs are short, and take shorter time to be translated.
They are easy to lean, understand and use.
They are easy to debug (correct/remove errors), & maintain.
High level language programs are easy to modify, and also to incorporate additional features thus enhancing its functional capabilities.
They are ‘user-friendly’ & problem-oriented; hence, can be used to solve problems arising from the real world.
They enable programmers to adapt easily to new hardware. This is because; they don’t have to worry about the hardware design of the computer.
High-level language programs are self-documenting, i.e., the program statements displays the transparency of purpose making the verification of the program easy.
High level languages are more flexible; hence, they enhance the creativity of the programmer and increase his/her productivity in the workplace.

Disadvantages of using High-level languages

High-level languages are not machine-oriented; hence, they do not use of the CPU and hardware facilities efficiently.
The languages are machine-independent, and cannot be used in programming the hardware directly.
Each high-level language statement converts into several machine code instructions. This means that, they use more storage space, and it also takes more time to run the program.
Their program statements are too general; hence, they execute slowly than their machine code program equivalents.
They have to be interpreted or compiled to machine-readable form before the computer can execute them.
The languages cannot be used on very small computers.
The source program written in a high-level language needs a Compiler, which is loaded into the main memory of the computer, and thus occupies much of memory space. This greatly reduces the memory available for a source program.

TYPES OF HIGH-LEVEL LANGUAGES

High-level languages are classified into five different groups:

Third generation languages (Structured / Procedural languages).
Fourth generation languages (4GLs).
Fifth generation languages (5GLs)
Object-oriented programming languages (OOPs).
Web scripting languages.

The various types of high-level languages differ in:

The data structures they handle.
The control structures they support.
The assignment instructions they use.
Application areas, e.g., educational, business, scientific, etc.

STRUCTURED LANGUAGES

A structured (procedural) language allows a large program to be broken into smaller sub-programs called modules, each performing a particular (single) task. This technique of program design is referred to as structured programming.

Structured programming also makes use of a few simple control structures in problem solving. The 3 basic control structures are:

Sequence
Selection.
Iteration (looping).

Advantages of structured programming.

It is flexible.
Structured programs are easier to read.
Programs are easy to modify because; a programmer can change the details of a section without affecting the rest of the program.
It is easier to document specific tasks.
Use of modules that contain standard procedures throughout the program saves development time.
Modules can be named in such a way that, they are consistent and easy to find in documentation.
Debugging is easier because; each module can be designed, coded & tested independently.

Examples of Third generation programming languages include:

BASIC (Beginners All-purpose Symbolic Instructional Code).
BASIC is a simple general-purpose high-level language used in most computer processing tasks such as developing business and educational applications.
It is easy to learn & use; hence, suitable for students who wish to easily learn programming.
Translation in most versions of BASIC is carried out by an Interpreter.
Disadvantages of BASIC.
-BASIC is available in so many versions with different dialects/languages & therefore, it has no standard.
-Some dialects are limited to data & control structures they support.
-Some versions of BASIC offer limited facilities in terms of structured programming & meaningful variable names.
PASCAL
PASCAL is a general-purpose, high-level programming language, which was named after a French mathematician called Blaise Pascal.
It was developed as an academic tool to help in the teaching and learning of structured programming.
PASCAL supports structured programming, i.e., it uses procedures & functions, which allow a ‘top-down’ approach to solving problems.
-It is not easy to learn because; it has strict rules in its grammar on typing of variables (data names) & declarations.
-It is poor (has limited ability) on handling of data files.
COBOL (Common Business Oriented Language)
COBOL is designed for developing programs that solve business problems, e.g., can be used to develop commercial data processing applications such as computer-based inventory control systems. COBOL is mostly used where large amounts of data are to be handled, because it supports powerful data & control structures. COBOL programs are semi-compiled, and the intermediate code is interpreted. A program written in COBOL language consists of 4 divisions: -
(i). Identification division: Where the programmer & the program details are specified, e.g., program ID, programmer name, etc.
(ii). Environment division: Where the equipment to be used by the source & the object programs are defined, e.g., the computer hardware.
(iii). Data division: Where the various files to be used by the program are described, e.g., a description of the input files.
(iv). Procedure division: Where all the procedures required to manipulate/interrelate the data into information are defined.
Advantages of COBOL.
-It is easy to read.
-It is portable, i.e., can be used on different types of computers. This is because; it has an American National Institute standard.
American National Standards Institute (ANSI): – An international organization that devised/ invented the group of standardized symbols used in flowcharting.
-It is widely used, and has a pool of skilled programmers.
Disadvantage of COBOL.
The structure of a COBOL program is too long even for simple programs.
E.g., consider the following assignment statement:
DIVIDE A into B giving C.
This statement when used in BASIC language can much short ‘C=A/B’. However, notice that the COBOL statement above is more self defining.
FORTRAN (FORmula TRANslator)
It was developed for mathematicians, scientists and engineers. It provides an easier way of writing scientific & engineering applications.
FORTRAN statements are mostly in form of mathematical expressions; hence, it is useful in writing of programs that can process numeric data.
FORTRAN programs are compiled.
Advantages of FORTRAN.
-It is portable, i.e. it can be used on different types of computers.
Disadvantage of FORTRAN.
It is not suited for business applications.
Ada
This language was named after the first lady programmer Ada Lovelace.
It is suitable for developing military, industrial and real-time systems.
C
C is mainly used for developing system software such as the operating system as well as developing the application packages.
It has powerful commands that permit the rapid development of programs, and allows direct control over the hardware.
Disadvantage of C
It is difficult to read & learn because of its strict dialect rules.
LOGO
LOGO was designed for educational use in which children can explore & develop concepts through programming the movement of a pen.
COROL
COROL is used in Real-time processing.
COROL programs are compiled.
RPG (Report Program Generator)
RPG is used in report generating applications, (i.e. it is designed to facilitate the output of reports of business data).
A Report generator is a software tool that extracts stored data to create customized reports that are not normally/usually produced by existing applications.
SNOBOL (String Oriented Symbolic Language).
It is a high-level language designed to manipulate strings of characters. It is therefore used for non-numeric applications.

FOURTH GENERATION LANGUAGES (4GL’S).

4GLs make programming even easier than the 3GLs because; they present the programmer with more programming tools, such as command buttons, forms, textboxes etc. The programmer simply selects graphical objects called controls on the screen, and then uses them to create designs on a form by dragging a mouse pointer.

The languages also use application generators (which in the background) to generate the necessary program codes; hence, the programmer is freed from the tedious work of writing the code.

4GLs are used to enquire & access the data stored in database systems; hence, they are described as the Query languages.

Purpose of fourth generation languages.

The 4GL’s were designed to meet the following objectives: -

To speed up the application-building process, thereby increasing the productivity of a programmer.
To enable quick & easy amendments and alteration of programs.
To reduce development & maintenance costs.
To make languages user-friendly. This is because, the 4GL’s are designed to be user-oriented, unlike the 3rd generation languages which are problem & programmer oriented.
To allow non-professional end-users to develop their own solutions.
To generate bug-free codes from high-level expressions of requirements.

Examples of 4GLs are:

Visual Basic
Delphi Pascal
Visual COBOL (Object COBOL)
Access Basic

Advantages of fourth generation languages.

They are user-based, and therefore, easy to learn & understand.
The grammar of 4GL’s is very close to the natural English language. It uses menus & prompts to guide a non-specialist to retrieve data with ease.
Very little training is required in order to develop & use 4GL programs.
They provide features for formatting of input, processing, & instant reporting.

FIFTH GENERATION LANGUAGES (5GL’S).

The 5GL’s are designed to make a computer solve a problem by portraying human-like intelligence.

The languages are able to make a computer solve a problem for the programmer; hence, he/she does not spend a lot of time in coming up with the solution. The programmer only thinks about what problem needs to be solved and what conditions need to be met without worrying about how to implement an algorithm to solve the problem.

5GLs are mostly used in artificial intelligence.

Examples of 5GLs are:

PROLOG
LISP
Mercury
OCCAM.

LISP (LISt Processing)
In LISP, both programs & data are arranged (structured) as lists.
It is used in artificial intelligence. However, it is not suitable for commercial data processing applications.
PROLOG (PROgramming in LOGic)
PROLOG was developed from LISP by the Japanese.
It is designed for use with Expert systems & Artificial Intelligence. It is mostly used for solving problems, which involve objects and relationships between objects.
Like LISP, it is not suitable for commercial data processing applications.

OBJECT-ORIENTED PROGRAMMING LANGUAGES (OOPs)

Object-Oriented Programming is a new approach to software development in which data & procedures that operate on data are combined into one object.
OOPs use objects. An Object is a representation of a software entity such as a user-defined window or variable. Each object has specific data values that are unique to it (called state) and a set of the things it can accomplish called (functions or behaviour).
Several objects can be linked together to form a complete program. Programs send messages to an object to perform a procedure that is already embedded in it. This process of having data and functions that operate on the data within an object is called encapsulation.
The data structure & behaviour of an object is specified/described by a template (called a class). Classes are hierarchical, and it is possible to pass the data & behaviour of an object in one class down the hierarchy.
Object-Oriented programming enables rapid program development. Every object has properties such as colour, size, data source, etc, which can be set easily without much effort. In addition, every object has events associated with it that can be used to trigger certain actions, e.g. remove the window from the screen on clicking the ‘Close’ button.
OOP has contributed greatly to the development of graphical user interface operating systems and application programs.

Examples of Object-oriented programming languages are: -

Simula
C++
SmallTalk
Java

Java is sometimes associated with development of websites, but it can be used to create whole application programs that do not need a web browser to run.

JAVA

Java is an OOP language that resembles Object C (a simplified form of C++).
The code of Java displays graphics, accesses the network, and interfaces with users via a set of capabilities known as classes. Classes define similar states & common methods for the behavior of an object.
JAVA programs are not compiled into machine code; instead, they are converted into a collection of bytes that represent the code for an abstract Java Virtual machine (VM). A Java interpreter running on a physical machine is then used to translate those bytes into local actions, such as printing a string or drawing a button.

WEB SCRIPTING LANGUAGES.

Web scripting languages are mostly used to create or add functionalities on web pages.
Web pages are used for creating Web sites on the Internet where all sorts of advertising can be done.
Web pages are hypertext (plain-text) documents written using a language called HyperText Markup Language (HTML). HTML documents have a file extension of .Html or .Htm.
Note. HTML doesn’t have the declaration part and control structures, and has many limitations. Therefore, to develop functional websites, it must be used together with other web scripting languages like JavaScript, VBScript and Hypertext Preprocessor.

Comparison of Programming languages.

Machine language

Instruction set is made up of binary digits (0’s & 1’s).
Instruction is made of 2 parts: operation code & operand.
No translation is needed. (This is the computer language; hence, the computer understands it directly).
Executed by the hardware directly & is faster.
Difficult to learn, develop & maintain.
Programs are lengthy & tedious.
It is time-consuming to develop machine code programs.
Used in applications where efficient use of the CPU time is necessary, e.g., developing Operating systems & other Control programs that coordinate the working of peripherals.

Assembly language

Instruction set is made up of Mnemonics & labels.
Instruction is made up of 2 parts: operation code & operand, but comments can be added.
Uses an Assembler to convert the assembly language source codes to their object code equivalents
Executed faster than High-level, but slower than the machine code programs.
It’s easier to learn, develop & maintain as compared to machine code programs.
Like machine code language, the programs are lengthy & tedious.
They take a shorter time to develop as compared to machine code programs, but take longer than High-level language programs.
Like machine language, Assembly language programs are used in applications where efficient use of the CPU time is necessary.

High-level languages

Instruction set is similar to English language statements & mathematical operators.
The instruction varies depending on the particular language.
Uses compiler or interpreter - Compiler translates all the source code at once into object code; Interpreter translates line by line.
Translation & execution is very slow.
Easy to learn, develop, maintain and use.
Programs are shorter & simpler than Machine & assembly lang. programs.
Developing High-level language programs takes very short time.
Most High-level languages are general-purpose, & can be used to do almost all computer-processing tasks.

Factors to consider when choosing a Programming language.

The following factors should be considered when choosing a Programming language to use in solving a problem:

The availability of the relevant translator
Whether the programmer is familiar with the language
Ease of learning and use
Purpose of the program,
i.e., application areas such as education, business, scientific, etc.
Execution time
Applications that require quick response are best programmed in machine code or assembly language. High-level languages are not suitable for such application because, they take long to be translated & executed.
Development time
Development time is the time a programmer takes to write and run a program. - High-level languages are easy to read, understand and develop; hence, they require less development time. Machine code & Assembly languages are relatively difficult to read, understand and develop; hence, they are time-consuming.
Popularity
The language selected should be suitable and/or successful in the market with respect to the problems to be solved.
Documentation
It should have accompanying documentation (descriptions) on how to use the language or maintain the programs written in the language.
Maintenance
Programs are developed to solve specific problems, and the problems keep on changing; hence, the programs are also changed to perform the new functions. Program maintenance is the activity of incorporating more routines onto the program, modifying the existing routines or removing the obsolete routines to make the program adapt to a functionally enhanced environment. The maintenance is made easier if the language used is easy to read and understand.
Availability of skilled programmers
The language selected should have a pool of readily available programmers to ease the programming activity, and reduce development time.

Review Questions

(a). What is a Programming language?
(b). Explain the two levels of programming languages.
(a). What is meant by ‘Machine language’?
(b). Explain why machine language programming is so error-prone.
(c). Show the difference between Machine language and Assembly language.
(d). Give two advantages & three disadvantages of Machine language programming.
(a). What are High-level languages?
(b). Give the features/characteristics of high-level programming languages.
(c). Describe briefly how a program written in high-level programming language becomes a machine code program ready for operational use.
(d). Explain the advantages and disadvantages of using a High-level programming language for writing a program.
(e). List four examples of high-level programming languages. Indicate the application of each language in computing.
(a). What is meant by program portability?
(b). Why are low-level languages not considered to be portable?
List 8 factors that need to be considered when selecting a programming language.

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