What is a Programming Language?

A programming language is a stylized communication technique intended to be used for controlling the behaviour of a machine (often a computer). Like human languages programming languages have syntactic and semantic rules used to define meaning.

Thousands of different programming languages have been created and new ones are created every year. Few languages ever become sufficiently popular that they are used by more than a few people.

A professional programmer is likely to use dozens of different languages during their career. Job adverts usually specify which languages the applicant should be familiar, or fluent, in. Debates on the best programming language are often intense.

Definitions of Programming Language

There is no universally agreed definition for the term programming language. The following is a list of some of the methods that have been used to categorise a language as being a programming language.

• What it is used for. For instance, a programming language is a language used to write programs.
• Those involved in the interaction. For instance, a programming language differs from natural languages in that natural languages are used for interaction between people, while programming languages are used for communication from people to machines (this rules out languages used for computer to computer interaction).
• The constructs it contains. For instance, a programming language contains constructs for defining and manipulating data structures, and for controlling the flow of execution.
• Its expressive power. The theory of computation provides a classification of languages based on the range of computations expressible by them, with the most expressive language being one that is Turing complete (the language needs to contain at least a looping construct and a method of storing values, ie, variables). Any program that can be written in a language that is Turing complete can also be written in another language that is Turing complete. Some examples of languages that are not Turing complete are pure HTML (the use of embedded PHP or Javascript makes it Turing complete) and SQL (SQL vendors invariably add language extensions that create a Turing complete language).