Closing nested structures in the right order

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Quick Questions

Shade in the A or B circle for each question.

1. An IF sits inside a REPEAT. Which end line comes first?

A END IF, then END REPEAT

B END REPEAT, then END IF

2. Which rule is correct for pseudocode blocks?

A Each IF needs its own END IF

B One END IF can close several IF lines

3. A REPEAT 5 TIMES loop has no END REPEAT. What is this?

A An error, because the loop is never closed

B Fine, because the loop ends by itself

4. Which pseudocode closes its blocks correctly? REPEAT 3 TIMES IF score > 5 THEN SAY "Win"

A Add END REPEAT, then END IF

B Add END IF, then END REPEAT

5. Which line does this END IF match? REPEAT UNTIL lives = 0 IF hit = true THEN lives ← lives - 1 END IF END REPEAT

A It matches REPEAT UNTIL lives = 0

B It matches IF hit = true THEN

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1REPEAT 5 TIMES IF score > 10 THEN SAY "Win" END IF END REPEAT		AThe END IF is missing. The IF block is never closed, which is an error. Add END IF before END REPEAT.
2END REPEAT		BThe IF is inside the loop, so END IF closes first and END REPEAT closes last.
3Each IF needs its own END IF, even when the IF sits inside a loop.		CThe end lines are in the wrong order. The innermost block (IF) must be closed first, so END IF goes before END REPEAT.
4Close the innermost structure first, then the outer one, so the end lines match their opening lines like a stack.		DCloses the REPEAT loop that was opened earlier. It must match a REPEAT line and come after any inner END IF.
5REPEAT 4 TIMES IF x > 5 THEN SAY "Big" END REPEAT		EREPEAT UNTIL lives = 0 IF hit = true THEN lives ← lives - 1 END IF END REPEAT
6REPEAT 4 TIMES IF x > 5 THEN SAY "Big" END REPEAT END IF		FREPEAT 3 TIMES IF age >= 13 THEN SAY "Teen" END IF END REPEAT

Definitions

END IF / END REPEAT

Fill in the Blanks

Complete each line of code by filling in the missing parts.

SET score TO score + 1 ______ END REPEAT

SET score TO score + 1 END IF __________

IF lives = 0 THEN SAY "Game over" ______

______ 3 TIMES SAY "Hi" END REPEAT

SAY "Done" END IF END ______

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A SET total TO 0

B IF total < 10 THEN

C IF total < 10 THEN

D ADD 2 TO total

E END IF

F END REPEAT

Question 2

A SET n TO 0

B REPEAT 3 TIMES

C REPEAT 2 TIMES

D SAY "Low"

E END IF

F END REPEAT

Question 3

A REPEAT 5 TIMES

B IF key = "w" THEN

C SAY "Go"

D END REPEAT

E END REPEAT

Question 4

A REPEAT 2 TIMES

B REPEAT 3 TIMES

C SAY "Welcome"

D END REPEAT

E END IF

Question 5

A SET lives TO 3

B IF lives > 0 THEN

C IF lives > 1 THEN

D SAY "Go"

E END REPEAT

F END IF

Answer Key

Closing nested structures in the right order

Section A: Quick Questions

A — END IF, then END REPEAT

A — Each IF needs its own END IF

A — An error, because the loop is never closed

B — Add END IF, then END REPEAT

B — It matches IF hit = true THEN

Section B: Match the Pairs

REPEAT 5 TIMES IF score > 10 THEN SAY "Win" END IF END REPEAT → The IF is inside the loop, so END IF closes first and END REPEAT closes last.

END REPEAT → Closes the REPEAT loop that was opened earlier. It must match a REPEAT line and come after any inner END IF.

Each IF needs its own END IF, even when the IF sits inside a loop. → REPEAT 3 TIMES IF age >= 13 THEN SAY "Teen" END IF END REPEAT

Close the innermost structure first, then the outer one, so the end lines match their opening lines like a stack. → REPEAT UNTIL lives = 0 IF hit = true THEN lives ← lives - 1 END IF END REPEAT

REPEAT 4 TIMES IF x > 5 THEN SAY "Big" END REPEAT → The END IF is missing. The IF block is never closed, which is an error. Add END IF before END REPEAT.

REPEAT 4 TIMES IF x > 5 THEN SAY "Big" END REPEAT END IF → The end lines are in the wrong order. The innermost block (IF) must be closed first, so END IF goes before END REPEAT.

Section C: Definitions

END IF / END REPEAT — Each IF and each REPEAT needs its own end line. Close the innermost block first, so END IF comes before END REPEAT when an IF is inside a loop. A missing end line is an error.

Section D: Fill in the Blanks

    SET score TO score + 1
  END IF
END REPEAT

    SET score TO score + 1
  END IF
END REPEAT

IF lives = 0 THEN
  SAY "Game over"
END IF

REPEAT 3 TIMES
  SAY "Hi"
END REPEAT

    SAY "Done"
  END IF
END REPEAT

Section E: Spot the Error

B — Line 2 opens a second IF, but the outer block is closed by END REPEAT. It should be REPEAT 4 TIMES so that END REPEAT has a REPEAT to match.

C — Line 3 opens a REPEAT, but it is closed by END IF, so the end line does not match its opening line. It should be IF n < 2 THEN.

D — The innermost block must be closed first. The IF is still open on line 4, so this line should be END IF, and END REPEAT comes last on line 5.

A — Line 1 opens a REPEAT, but the last line is END IF, so the outer end line has nothing to match. Line 1 should be IF hasTicket = 1 THEN.

C — Line 3 opens an IF, but it is closed by END REPEAT. The inner block should be REPEAT lives TIMES so the END REPEAT matches it.