What does “:=” do?

Question

I\'ve seen := used in several code samples, but never with an accompanying explanation. It\'s not exactly possible to google its use without knowing the proper

Answer 1

http://en.wikipedia.org/wiki/Equals_sign#In_computer_programming

In computer programming languages, the equals sign typically denotes either a boolean operator to test equality of values (e.g. as in Pascal or Eiffel), which is consistent with the symbol's usage in mathematics, or an assignment operator (e.g. as in C-like languages). Languages making the former choice often use a colon-equals (:=) or ≔ to denote their assignment operator. Languages making the latter choice often use a double equals sign (==) to denote their boolean equality operator.

Note: I found this by searching for colon equals operator

Answer 2

Colon-equals was used in Algol and its descendants such as Pascal and Ada because it is as close as ASCII gets to a left-arrow symbol.

The strange convention of using equals for assignment and double-equals for comparison was started with the C language.

In Prolog, there is no distinction between assignment and the equality test.

Answer 3

It's the assignment operator in Pascal and is often used in proofs and pseudo-code. It's the same thing as = in C-dialect languages.

Historically, computer science papers used = for equality comparisons and ← for assignments. Pascal used := to stand in for the hard-to-type left arrow. C went a different direction and instead decided on the = and == operators.

Answer 4

In a lot of CS books, it's used as the assignment operator, to differentiate from the equality operator =. In a lot of high level languages, though, assignment is = and equality is ==.