Question

The grid below contains a robot represented as a triangle, initially facing toward the top of the grid. The robot can move into a white or gray square but cannot move into a black region.

The code segment below uses the procedure goalReached, which evaluates to true if the robot is in the gray square and evaluates to false otherwise.
REPEAT UNTIL(goalReached())
{
<MISSING CODE>
}

Question
12

Mark for Review

Which of the following replacements for <MISSING CODE> can be used to move the robot to the gray square?

IF(CAN_MOVE(left))
{
ROTATE_LEFT()
MOVE_FORWARD()
}
Option A,IF(CAN_MOVE(left)) { ROTATE_LEFT() MOVE_FORWARD() }

IF(CAN_MOVE(forward))
{
MOVE_FORWARD()
ROTATE_LEFT()
}
Option B,IF(CAN_MOVE(forward)) { MOVE_FORWARD() ROTATE_LEFT() }

IF(CAN_MOVE(left))
{
ROTATE_LEFT()
}
MOVE_FORWARD()
Option C,IF(CAN_MOVE(left)) { ROTATE_LEFT() } MOVE_FORWARD()

IF(CAN_MOVE(forward))
{
MOVE_FORWARD()
}
ELSE
{
ROTATE_LEFT()
}

Answer 1

To determine which of the provided code options can effectively move the robot to the gray square, we need to analyze how the robot's movement works, given its direction and potential obstacles.

1. **Understanding Robot Movement**:
- The robot can turn left or move forward.
- It can only occupy white or gray squares and cannot enter black regions.
- The code needs to move the robot towards the gray square while ensuring it is not blocked.

2. **Evaluating Each Option**:
- **Option A**:
```plaintext
IF(CAN_MOVE(left))
{
ROTATE_LEFT()
MOVE_FORWARD()
}
```
- This option first checks if it can turn left; if so, it turns left and moves forward. This might help if turning left moves it into a valid path, but it doesn't account for moving forward in the primary direction.

- **Option B**:
```plaintext
IF(CAN_MOVE(forward))
{
MOVE_FORWARD()
ROTATE_LEFT()
}
```
- This checks if it can move forward first. If yes, it moves forward, then rotates left. However, if the gray square is directly in front, this would not pursue that direction effectively since it rotates left after the move.

- **Option C**:
```plaintext
IF(CAN_MOVE(left))
{
ROTATE_LEFT()
}
MOVE_FORWARD()
```
- In this case, if it can move left, it turns left and then moves forward. This option seems less effective since it moves forward immediately after the potential rotation, ignoring the immediate direction.

- **Fourth Option**:
```plaintext
IF(CAN_MOVE(forward))
{
MOVE_FORWARD()
}
ELSE
{
ROTATE_LEFT()
}
```
- This option first attempts to move forward; if it can't, it rotates left. This allows for direct movement towards the gray square and a backup plan if the forward path is blocked.

3. **Conclusion**:
- **Best Option**: The fourth option works best to prioritize moving toward the gray square directly and only rotate if there's an obstacle.

Therefore, the correct choice to replace `<MISSING CODE>` to move the robot to the gray square is:
```plaintext
IF(CAN_MOVE(forward))
{
MOVE_FORWARD()
}
ELSE
{
ROTATE_LEFT()
}
```