The BFS algorithm uses:

• open[x] to store whether vertex x has been added to the queue. If open[x] = true then x has not been added.
• d[x] to store the distance of x from S
• pred[x] to refer to the predecessor of x in the breadth-first tree

Note that the following pseudo-code uses indenting to indicate block structure. That is, consecutive statements at the same indentation level are all to be executed in the same block.