Difference between := and ← in pseudocode

This is a snippet from some pseudocode for a sorting algorithm. In it, the symbol ← is used to denote assignment, for example for the variable done. However, in the while loop the statement done:= false is written. I would assume it is also an assignment statement but I suspect it means somethings else, or perhaps extra, since if not, the ← would have simple be used again.

Algorithm MyAlgorithm(A, n)
Input: Array of integer containing n elements
Output: Possibly modified Array A

done ← true
j ← 0
while j ≤ n - 2 do
if A[j] > A[j + 1] then
swap(A[j], A[j + 1])
done:= false
j ← j + 1

-
This appears to be a slip-up in writing the code. At first I thought the arrow may denote "declare + define", whereas := would denote "redefine", but it's clear that j is redefined using the arrow below. In general, := is an assignment in pseudocode; to be honest, I've never seen the arrow in actual pseudocode. –  Eric Jan 17 '13 at 17:09
@Eric You should put this as an answer, I think it's as much an answer as it gets. However, I've seen ← as assignment (and use it myself) quite a lot. As long as people are consistent, it doesn't really matter much, as the given pseudocode obviously isn't. –  Pål GD Jan 17 '13 at 17:17
@PålGD Posted it, with an extra reference to Wikipedia. It's worth noting that they do recognize both the arrow and :=, though they mention that := is "more common". –  Eric Jan 17 '13 at 17:21

1 Answer

The use of := in this context appears to be a slip-up from whomever it is who wrote that pseudocode. The initial impression given is that they have different meanings (I thought at first that := was perhaps "redefine", and that ← was "declare and define"). However, with the use of j ← j + 1 on the line following it, it seems clear that the := was a mistake.

In general, := and = are the most common assignment operators, seemingly in both pseudocode and real code. You may be interested in looking at notations of the assignment operator in various programming languages, which include :=, =, <-, ←, and many others.

-
Thanks for that, I let my professor know. –  Imray Jan 17 '13 at 17:32