Syntax (programming languages) in the context of Undefined value

A file format is the way that information is encoded for storage in a computer file. It may describe the encoding at various levels of abstraction including low-level bit and byte layout as well high-level organization such as markup and tabular structure. A file format may be standarized (which can be proprietary or open) or it can be an ad hoc convention.

Some file formats are designed for very particular types of data: PNG files, for example, store bitmapped images using lossless data compression. Other file formats, however, are designed for storage of several different types of data: the Ogg format can act as a container for different types of multimedia including any combination of audio and video, with or without text (such as subtitles), and metadata. A text file can contain any stream of characters, including possible control characters, and is encoded in one of various character encoding schemes. Some file formats, such as HTML, scalable vector graphics, and the source code of computer software are text files with defined syntaxes that allow them to be used for specific purposes.

In computer programming, an operator is a programming language construct that provides functionality that may not be possible to define as a user-defined function (i.e. sizeof in C) or has syntax different than a function (i.e. infix addition as in a+b). Like other programming language concepts, operator has a generally accepted, although debatable meaning among practitioners while at the same time each language gives it specific meaning in that context, and therefore the meaning varies by individual language.

Some operators are represented with symbols – characters typically not allowed for a function identifier – to allow for presentation that is more familiar looking than typical function syntax. For example, a function that tests for greater-than could be named gt, but many languages provide an infix symbolic operator so that code looks more familiar. For example, this:

A "Hello, World!" program is usually a simple computer program that emits (or displays) to the screen (often the console) a message similar to "Hello, World!". A small piece of code in most general-purpose programming languages, this program is used to illustrate a language's basic syntax. Such a program is often the first written by a student of a new programming language, but it can also be used as a sanity check to ensure that the computer software intended to compile or run source code is correctly installed, and that its operator understands how to use it.

In programming, a class is a syntactic entity structure used to create objects. The capabilities of a class differ between programming languages, but generally the shared aspects consist of state (variables) and behavior (methods) that are each either associated with a particular object or with all objects of that class.

Object state can differ between each instance of the class whereas the class state is shared by all of them. The object methods include access to the object state (via an implicit or explicit parameter that references the object) whereas class methods do not.

Java is a high-level, general-purpose, memory-safe, object-oriented programming language. It is intended to let programmers write once, run anywhere (WORA), meaning that compiled Java code can run on all platforms that support Java without the need to recompile. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture. The syntax of Java is similar to C and C++, but has fewer low-level facilities than either of them. The Java runtime provides dynamic capabilities (such as reflection and runtime code modification) that are typically not available in traditional compiled languages.

Java gained popularity shortly after its release, and has been a popular programming language since then. Java was the third most popular programming language in 2022 according to GitHub. Although still widely popular, there has been a gradual decline in use of Java in recent years with other languages using JVM gaining popularity.

In computer science, an expression is a syntactic notation in a programming language that may be evaluated to determine its value of a specific semantic type. It is a combination of one or more numbers, constants, variables, functions, and operators that the programming language interprets (according to its particular rules of precedence and of association) and computes to produce ("to return", in a stateful environment) another value.In simple settings, the resulting value is usually one of various primitive types, such as string, boolean, or numerical (such as integer, floating-point, or complex).

Expressions are often contrasted with statements—syntactic entities that have no value (an instruction).

A programming paradigm is a relatively high-level way to conceptualize and structure the implementation of a computer program. A programming language can be classified as supporting one or many paradigms.

Paradigms are separated along and described by different dimensions of programming. Some paradigms are about implications of the execution model, such as allowing side effects, or whether the sequence of operations is defined by the execution model. Other paradigms are about the way code is organized, such as grouping into units that include both state and behavior. Yet others are about syntax and grammar.

Bash (short for "Bourne Again SHell") is an interactive command interpreter and scripting language developed for Unix-like operating systems. Created in 1989 by Brian Fox for the GNU Project, it is designed as a completely free software alternative for the Bourne shell, sh, and other proprietary Unix shells, supported by the Free Software Foundation. Having gained widespread adoption, Bash is commonly used as the default login shell for numerous Linux distributions. It also supports the execution of commands from files, known as shell scripts, facilitating automation.

The Bash command syntax is a superset of the Bourne shell's syntax, from which all basic features of the Bash syntax were copied. As a result, Bash can execute the vast majority of Bourne shell scripts without modification. Some other ideas were borrowed from the C shell, its successor tcsh, and the Korn Shell. It is available on nearly all modern operating systems, making it a versatile tool in various computing environments.

A command language is a language for job control in computing. It is a domain-specific and interpreted language; common examples of a command language are shell or batch programming languages.

These languages can be used directly at the command line, but can also automate tasks that would normally be performed manually at the command line. They share this domain—lightweight automation—with scripting languages, though a command language usually has stronger coupling to the underlying operating system. Command languages often have either very simple grammars or syntaxes very close to natural language, making them more intuitive to learn, as with many other domain-specific languages.

In computer programming, a statement is a syntactic unit of an imperative programming language that expresses some action to be carried out. A program written in such a language is formed by a sequence of one or more statements. A statement may have internal components (e.g. expressions).

Many programming languages (e.g. Ada, Algol 60, C, Java, Pascal) make a distinction between statements and definitions/declarations. A definition or declaration specifies the data on which a program is to operate, while a statement specifies the actions to be taken with that data.

A syntax error is a mismatch in the syntax of data input to a computer system that requires a specific syntax. For source code in a programming language, a compiler detects syntax errors before the software is run (at compile-time), whereas an interpreter detects syntax errors at run-time. A syntax error can occur based on syntax rules other than those defined by a programming language. For example, typing an invalid equation into a calculator (an interpreter) is a syntax error.

Some errors that occur during the translation of source code may be considered syntax errors by some but not by others. For example, some say that an uninitialized variable in Java is a syntax error, but others disagree – classifying it as a static semantic error.

In computer programming, a block of source code is a grouping of statements that execute in sequential order, top to bottom. The block structure is fundamental to structured programming, where control structures are formed with blocks. Syntactically, a block acts much like a single statement in that a control structure generally operates either on a single statement or a block.

The nature of a block varies by programming language, but there are typical features. A block usually provides for visibility scope such that an identifier defined in a block is not visible in outer, containing blocks, but is visible in inner, nested blocks unless it is masked by an identifier with the same name. A block usually provides for lifetime scope such that resources associated with an identifier are partially or fully released when control flow reaches the end of the block in which the identifier was defined.

A regular expression (shortened as regex or regexp), sometimes referred to as a rational expression, is a sequence of characters that specifies a match pattern in text. Usually such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation. Regular expression techniques are developed in theoretical computer science and formal language theory.

The concept of regular expressions began in the 1950s, when the American mathematician Stephen Cole Kleene formalized the concept of a regular language. They came into common use with Unix text-processing utilities. Different syntaxes for writing regular expressions have existed since the 1980s, one being the POSIX standard and another, widely used, being the Perl syntax.

This article compares the syntax of many notable programming languages.

ALGOL (/ˈælɡɒl, -ɡɔːl/; short for "Algorithmic Language") is a family of imperative computer programming languages originally developed in 1958. ALGOL heavily influenced many other languages and was the standard method for algorithm description used by the Association for Computing Machinery (ACM) in textbooks and academic sources for more than thirty years.

In the sense that the syntax of most modern languages is "Algol-like", it was arguably more influential than three other high-level programming languages among which it was roughly contemporary: FORTRAN, Lisp, and COBOL. It was designed to avoid some of the perceived problems with FORTRAN and eventually gave rise to many other programming languages, including PL/I, Simula, BCPL, B, Pascal, Ada, and C.

Simula is the name of two simulation programming languages, Simula I and Simula 67, developed in the 1960s at the Norwegian Computing Center in Oslo, by Ole-Johan Dahl and Kristen Nygaard. Syntactically, it is an approximate superset of ALGOL 60,and was also influenced by the design of SIMSCRIPT.

Simula 67 introduced objects, classes, inheritance and subclasses, virtual procedures, coroutines, and discrete event simulation, and featured garbage collection. Other forms of subtyping (besides inheriting subclasses) were introduced in Simula derivatives.