Concatenation

In formal language theory and computer programming, string concatenation is the operation of joining character strings end-to-end. For example, the concatenation of "snow" and "ball" is "snowball". In some but not all formalisations of concatenation theory, also called string theory, string concatenation is a primitive notion.

Syntax

In many programming languages, string concatenation is a binary infix operator. The + (plus) operator is often overloaded to denote concatenation for string arguments: "Hello, " + "World" has the value "Hello, World". In other languages there is a separate operator, particularly to specify implicit type conversion to string, as opposed to more complicated behavior for generic plus. Examples include . in Edinburgh IMP, Perl, and PHP, and & in Ada and Visual Basic. Other syntax exists, like || in PL/I and Oracle Database SQL.

In a few languages, notably C, C++, and Python, there is string literal concatenation, meaning that adjacent string literals are concatenated, without any operator: "Hello, " "World" has the value "Hello, World". In other languages, concatenation of string literals with an operator is evaluated at compile time, via constant folding.

Concatenation (disambiguation)

Concatenation may refer to:

See also

Concatenation (mathematics)

In mathematics, concatenation is the joining of two numbers by their numerals. That is, the concatenation of 123 and 456 is 123456. Concatenation of numbers a and b is denoted a||b. Relevant subjects in recreational mathematics include Smarandache-Wellin numbers, home primes, and Champernowne's constant. The convention for sequences at places such as the Online Encyclopedia of Integer Sequences is to have sequences of concatenations include as the first term a number prior to the actual act of concatenation. Therefore, care must be taken to ensure that parties discussing a topic agree either with this convention or with plain language. For example, the first term in the sequence of concatenations of increasing even numbers may be taken to be either 24, as would seem obviously correct, or simply 2, according to convention.

Calculation

The concatenation of numbers depends on the numeric base, which is often understood from context.

Given the numbers p and q in base b, the concatenation p||q is given by