Programming languages

April 2018

Programming language

A "programming language" is a language designed to describe a set of consecutive actions to be executed by a computer. A programming language is therefore a practical way for us (humans) to give instructions to a computer.

On the other hand, the term "natural language" defines a means of communication shared by a group of individuals (for example: English or French)

Languages that computers use to communicate with each other, have nothing to do with programming languages, they are referred to as communication protocols, these are two very different concepts. A programming language is very strict:

EACH instruction corresponds to ONE 
processor action.

The language used by the processor is called machine code. The code that reaches the processor consists of a series of 0s and 1s known as (binary data).

Machine code is therefore difficult for humans to understand, which is why intermediary languages, which can be understood by humans, have been developed. The code written in this type of language is transformed into machine code so that the processor can process it.

The assembler was the first programming language ever used. This is very similar to machine code but can be understood by developers. Nonetheless, such a language is so similar to machine code that it strictly depends on the type of processor used (each processor type may have its own machine code). Thus a program developed for one machine may not be ported to another type of machine. The term "portability" describes the ability to use a software program on different types of machines. A software program written in assembler code, may sometimes have to be completely rewritten to work on another type of computer!

A programming language has therefore several advantages:

it is much more understandable than machine code;
it allows greater portability, i.e. can be easily adapted to run on different types of computers.

Imperative and functional programming languages

Programming languages are generally divided into two major groups according to how their commands are processed:

imperative languages;
functional languages.

Imperative programming language

An imperative language programs using a series of commands, grouped into blocks and comprising of conditional statements which allow the program to return to a block of commands if the condition is met. These were the first programming languages in use, even today many modern languages still use this principle.

Structured imperative languages suffer, however, from lack of flexibility due to the sequentiality of instructions.

Functional programming language

A functional programming language (often called procedural language) is a language which creates programs using functions, returning to a new output state and receiving as input the result of other functions. When a function invokes itself, we refer to this as recursion.

Interpretation and compilation

Programming languages may be roughly divided into two categories:

interpreted languages
compiled languages

Interpreted language

A programming language is by definition different to machine code This must therefore be translated so that the processor can understand the code. A program written in an interpreted language requires an extra program (the interpreter) which translates the programs commands as needed.

Compiled language

A program written in a "compiled" language is translated by an additional program called a compiler which in turn creates a new stand-alone file which does not require any other program to execute itself, such a file is called an executable.

A program written in a compiled language has the advantage of not requiring an additional program to run it once it has been compiled. Furthermore, as the translation only needs to be done once, at compilation it executes much faster.
However, it is not as flexible as a program written in an interpreted language, as each modification of the source file (the file understandable by humans: the file to be compiled) means that the program must be recompiled for the changes to take effect.

On the other hand, a compiled program has the advantage of guaranteeing the security of the source code. In effect, interpreted language, being a directly legible language, means that anyone can find out the secrets of a program and thus copy or even modified the program. There is therefore a risk of copyright violation. On the other hand, certain secure applications need code confidentiality to avoid illegal copying (bank transactions, on-line payments, secure communications...).

Intermediary languages

Some languages belong to both categories (LISP, Java, Python...) as the program written in these languages may in certain cases undergo an intermediary compilation phase, into a file written in a language different to the source file and non-executable (requiring an interpreter). Java applets, small programs, often loaded in web pages, are compiled files, which can only be executed from within a web browser (these are files with the .class extension).

Some examples of widely used languages

Here is a non-exhaustive list of current programming languages:

Language	Main application area	Compiled/interpreted
ADA	Real-time	Compiled language
BASIC	Programming for educational purposes	Interpreted language
C	System programming	Compiled language
C++	System object programming	Compiled language
Cobol	Management	Compiled language
Fortran	Calculation	Compiled language
Java	Internet oriented programming	Intermediary language
MATLAB	Mathematical calculations	Interpreted language
Mathematica	Mathematical calculations	Interpreted language
LISP	Artificial intelligence	Intermediary language
Pascal	Education	Compiled language
PHP	Dynamic website development	Interpreted language
Prolog	Artificial intelligence	Interpreted language
Perl	Processing character strings	Interpreted language