Array bounds starting at zero or one

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. DECLARE Scores : ARRAY[0:29] OF INTEGER. What is the index of the first element?

A 0

B 1

2. DECLARE Names : ARRAY[1:30] OF STRING. Which element is the first one?

A Names[1]

B Names[0]

3. How many elements do ARRAY[0:29] and ARRAY[1:30] each hold?

A ARRAY[0:29] holds 29 and ARRAY[1:30] holds 30

B Both hold 30 elements

4. Which is the better practice when declaring an array in pseudocode?

A State the lower bound explicitly, such as ARRAY[1:30]

B Leave the lower bound out and let the computer assume it

5. Which lower bound does the Cambridge IGCSE syllabus generally use in its pseudocode?

A 0

B 1

Match the Pairs

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

Left column		Right column
1DECLARE Scores : ARRAY[0:29] OF INTEGER		AThe first index is 1 and the last is 30, so the array holds 30 elements
2DECLARE Scores : ARRAY[1:30] OF INTEGER		BDECLARE Names : ARRAY[1:20] OF STRING
3Stating the lower bound explicitly in the declaration shows whether the first element is at index 0 or 1		CARRAY[0:30] holds 31 elements (0 to 30). For 30 elements starting at 0, use ARRAY[0:29]. Or use ARRAY[1:30] to start at 1.
4In an array with lower bound 0, the first element is read using index 0		DOUTPUT Scores[0]
5DECLARE Marks : ARRAY[0:30] OF INTEGER // the student wants exactly 30 elements		EIndex 30 is out of range because the upper bound is 29. The last element is Marks[29], and the first is Marks[0].
6DECLARE Marks : ARRAY[0:29] OF INTEGER OUTPUT Marks[30]		FThe first index is 0 and the last is 29, so the array holds 30 elements

Definitions

ARRAY[1:30]

Fill in the Blanks

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

DECLARE Names : ARRAY[_:30] OF STRING

DECLARE Scores : ARRAY[0:__] OF INTEGER

DECLARE Marks : ARRAY[0:29] OF INTEGER OUTPUT Marks[_]

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

DECLARE Names : ARRAY[1:30] OF STRING OUTPUT Names[__]

Spot the Error

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

Question 1

A DECLARE S : ARRAY[5:1] OF REAL

B S[1] ← 7.5

C OUTPUT S[1]

Question 2

A DECLARE M : ARRAY[0:4] OF CHAR

B M[5] ← 'A'

C M[4] ← 'E'

D OUTPUT M[0]

Question 3

A DECLARE P : ARRAY[9] OF CHAR

B FOR I ← 0 TO 9

C P[I] ← '*'

D NEXT I

Question 4

A DECLARE T : ARRAY[1:9] OF CHAR

B FOR I ← 0 TO 9

C T[I] ← 'x'

D NEXT I

Question 5

A DECLARE W : ARRAY[1:3] OF CHAR

B W[1] ← 'a'

C W[0] ← 'c'

D OUTPUT W[1]

Answer Key

Array bounds starting at zero or one

Section A: Quick Questions

A — 0

A — Names[1]

B — Both hold 30 elements

A — State the lower bound explicitly, such as ARRAY[1:30]

B — 1

Section B: Match the Pairs

DECLARE Scores : ARRAY[0:29] OF INTEGER → The first index is 0 and the last is 29, so the array holds 30 elements

DECLARE Scores : ARRAY[1:30] OF INTEGER → The first index is 1 and the last is 30, so the array holds 30 elements

Stating the lower bound explicitly in the declaration shows whether the first element is at index 0 or 1 → DECLARE Names : ARRAY[1:20] OF STRING

In an array with lower bound 0, the first element is read using index 0 → OUTPUT Scores[0]

DECLARE Marks : ARRAY[0:30] OF INTEGER // the student wants exactly 30 elements → ARRAY[0:30] holds 31 elements (0 to 30). For 30 elements starting at 0, use ARRAY[0:29]. Or use ARRAY[1:30] to start at 1.

DECLARE Marks : ARRAY[0:29] OF INTEGER OUTPUT Marks[30] → Index 30 is out of range because the upper bound is 29. The last element is Marks[29], and the first is Marks[0].

Section C: Definitions

ARRAY[1:30] — The number before the colon is the lower bound, the first index. ARRAY[1:30] starts at 1, ARRAY[0:29] starts at 0. Both hold 30 elements, so always state the lower bound.

Section D: Fill in the Blanks

DECLARE Names : ARRAY[1:30] OF STRING

DECLARE Scores : ARRAY[0:29] OF INTEGER

DECLARE Marks : ARRAY[0:29] OF INTEGER
OUTPUT Marks[0]

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

DECLARE Names : ARRAY[1:30] OF STRING
OUTPUT Names[30]

Section E: Spot the Error

A — The lower bound must come first, before the colon, and the upper bound after it. It should be ARRAY[1:5], which holds 5 elements.

B — The bounds are 0 to 4, so index 5 is out of range. The first element is M[0], so the line should be M[0] ← 'A'.

A — The declaration must state both the lower and the upper bound, like [0:9]. Writing only one number does not say where the indexes start.

B — The lower bound is 1, so there is no T[0]. The loop would start at an index that does not exist. It should be FOR I ← 1 TO 9.

C — The lower bound is 1, so index 0 does not exist. The last element of ARRAY[1:3] is W[3], so the line should be W[3] ← 'c'.