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Fix the code

  1. move_left()
    Bug
    move_right()
    Fix

    Change only the wrong part

    You found the bug. Now fix it. The robot must go right 2. Line 2 says move_left(). Change only that line to move_right(). Keep the lines that work.

  2. move_up()
move_up()

    Add a missing line

    The robot must go up 2. The code had just one move_up(). Add one more move_up() line. Now it goes up 2.

  3. move_right()
repeat 5:
    move_right()

    Fix the loop number

    The star is 6 squares right. One move_right() comes before the loop. So the loop needs 5 more. 1 + 5 = 6.

  4. repeat 4 times
    move right
    repeat 3 times
    move up

    Test it again

    This code said repeat 3, and the robot bumped a rock. Change 3 to 4 to reach the gap. Press Run and watch. It reaches the flag, so the bug is gone.

  5. move_up()
move_right()
move_right()

    Two bugs

    Some code has two bugs. The robot must go up 1, then right 2. The code said down, right, left. Lines 1 and 3 were wrong. Here is the fixed code.

For parents

Goal: Your child learns to fix a bug by changing only the wrong part, then testing the code again.

  • Ask: which line is wrong? What should it say instead?
  • After a fix, have your child run the code again to check that the robot reaches the goal.
  • The labs after the cards hold real bugs. Let your child run the code first and watch where it goes wrong.

Away from the screen: Build a block tower from a drawing with one block wrong on purpose. Your child fixes only that block, then checks it against the drawing.

Coding · Debugging
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