Workshop › Chess › Step 20 of 48

The rook slides

What we are doing

A rook does not jump: it slides any distance in one of four directions until something stops it. So for each direction we keep stepping with a while loop: an empty square is a move; a piece ends the slide, and if it is an enemy it can be taken.

```js
const STRAIGHT = [[1, 0], [-1, 0], [0, 1], [0, -1]]

      if (kind === 'R') {
        for (const [dr, dc] of STRAIGHT) {
          let tr = r + dr
          let tc = c + dc
          while (inside(tr, tc)) {
            if (board[tr][tc]) {
              if (board[tr][tc][0] !== color) add(r, c, tr, tc)
              break
            }
            add(r, c, tr, tc)
            tr += dr
            tc += dc
          }
        }
      }
```

What it means

STRAIGHT lists the four straight directions as one-square steps.
while (inside(tr, tc)) repeats as long as the square is on the board.
On a piece: add a capture if it is an enemy, then break leaves the loop: nothing can pass through a piece.
Otherwise add the move and step one square further with +=.

Your turn

Under KING write STRAIGHT.
In pseudoMoves, under the closing } of the knight/king block (above the } that closes the c loop), write the rook block.

Skills: Loops

← Say whose turn it is Bishops and queens →

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