Looping with a lower bound of zero

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Quick Questions

Shade in the A or B circle for each question.

1. An array is declared as ARRAY[0:29] OF STRING. Which loop visits every element exactly once?

A FOR Index ← 1 TO 30

B FOR Index ← 0 TO 29

2. DECLARE Scores : ARRAY[0:9] OF INTEGER. Which loop header matches this declaration?

A FOR Index ← 0 TO 9

B FOR Index ← 1 TO 10

3. A student uses FOR Index ← 1 TO 30 on ARRAY[0:29]. What goes wrong?

A It skips element 0 and tries to use element 30, which is outside the array

B It works correctly because there are 30 loop repeats

4. For ARRAY[0:29], which loop starts at the lower bound?

A FOR Index ← 0 TO 29

B FOR Index ← 29 TO 0

5. Names is declared as ARRAY[0:4] OF STRING. Which loop goes outside the array?

A FOR Index ← 0 TO 4

B FOR Index ← 0 TO 5

Match the Pairs

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

Left column		Right column
1FOR Index ← 0 TO 29		AThe loop ends at 30, which is past the upper bound 29, so it goes out of range. It should end at 29.
2FOR Index ← 1 TO 30		BFOR Index ← 0 TO 9
3To loop through ARRAY[0:9], start at the lower bound and finish at the upper bound		CThe loop starts at 1, so element 0 is never visited. It should start at the lower bound 0.
4The loop limits must match the declaration of the array ARRAY[0:49]		DVisits every element of ARRAY[0:29] from the lower bound to the upper bound
5FOR Index ← 1 TO 29 (for ARRAY[0:29])		EMisses element 0 and goes past the end of ARRAY[0:29]
6FOR Index ← 0 TO 30 (for ARRAY[0:29])		FFOR Index ← 0 TO 49

Definitions

FOR Index ← 0 TO 29

Fill in the Blanks

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

DECLARE Scores : ARRAY[0:29] OF INTEGER FOR Index ← _ TO 29

DECLARE Names : ARRAY[0:29] OF STRING FOR Index ← 0 TO __

DECLARE Marks : ARRAY[0:9] OF INTEGER FOR Index ← 0 TO _ OUTPUT Marks[Index]

DECLARE Items : ARRAY[_:19] OF STRING FOR Index ← 0 TO 19

FOR Index ← 0 __ 29 OUTPUT Scores[Index] NEXT Index

Spot the Error

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

Question 1

A // Mark is ARRAY[0:9]

B FOR I ← 1 TO 9

C Mark[I] ← 0

D NEXT I

Question 2

A // Mark is ARRAY[0:29]

B FOR Index ← 1 TO 29

C OUTPUT Mark[Index]

D NEXT Index

Question 3

A // Temp is ARRAY[0:29]

B Total ← 0

C FOR Index ← 0 TO 30

D Total ← Total + Temp[Index]

E NEXT Index

Question 4

A // Score is ARRAY[0:29]

B FOR Index ← 0 TO 28

C Score[Index] ← 0

D NEXT Index

Question 5

A DECLARE T : ARRAY[0:8] OF REAL

B FOR I ← 0 TO 9

C T[I] ← 0.5

D NEXT I

Answer Key

Looping with a lower bound of zero

Section A: Quick Questions

B — FOR Index ← 0 TO 29

A — FOR Index ← 0 TO 9

A — It skips element 0 and tries to use element 30, which is outside the array

A — FOR Index ← 0 TO 29

B — FOR Index ← 0 TO 5

Section B: Match the Pairs

FOR Index ← 0 TO 29 → Visits every element of ARRAY[0:29] from the lower bound to the upper bound

FOR Index ← 1 TO 30 → Misses element 0 and goes past the end of ARRAY[0:29]

To loop through ARRAY[0:9], start at the lower bound and finish at the upper bound → FOR Index ← 0 TO 9

The loop limits must match the declaration of the array ARRAY[0:49] → FOR Index ← 0 TO 49

FOR Index ← 1 TO 29 (for ARRAY[0:29]) → The loop starts at 1, so element 0 is never visited. It should start at the lower bound 0.

FOR Index ← 0 TO 30 (for ARRAY[0:29]) → The loop ends at 30, which is past the upper bound 29, so it goes out of range. It should end at 29.

Section C: Definitions

FOR Index ← 0 TO 29 — For ARRAY[0:29], the loop must start at the lower bound 0 and end at the upper bound 29. It then visits all 30 elements and never goes outside the array.

Section D: Fill in the Blanks

DECLARE Scores : ARRAY[0:29] OF INTEGER
FOR Index ← 0 TO 29

DECLARE Names : ARRAY[0:29] OF STRING
FOR Index ← 0 TO 29

DECLARE Marks : ARRAY[0:9] OF INTEGER
FOR Index ← 0 TO 9
   OUTPUT Marks[Index]

DECLARE Items : ARRAY[0:19] OF STRING
FOR Index ← 0 TO 19

FOR Index ← 0 TO 29
   OUTPUT Scores[Index]
NEXT Index

Section E: Spot the Error

B — Mark has a lower bound of 0, so the loop must start at 0. Starting at 1 skips Mark[0]. The correct line is FOR I ← 0 TO 9.

B — The array runs from index 0 to 29. A loop starting at 1 misses element 0. The correct line is FOR Index ← 0 TO 29.

C — The upper bound is 29. Going up to 30 reads Temp[30], which is outside the array. The correct line is FOR Index ← 0 TO 29.

B — The loop stops one element early, so Score[29] is never set. It must run to the upper bound: FOR Index ← 0 TO 29.

A — The loop runs from 0 to 9, so the array needs an upper bound of 9. With [0:8], T[9] would be out of range. The declaration should be ARRAY[0:9].