Choosing a 1D or 2D array for a scenario

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. A teacher stores the names of 30 students in one simple list. Which array fits best?

A A 1D array, e.g. ARRAY[1:30] OF STRING

B A 2D array, e.g. ARRAY[1:30, 1:30] OF STRING

2. A noughts and crosses game board has 3 rows and 3 columns. Which array fits best?

A A 1D array, e.g. ARRAY[1:3] OF CHAR

B A 2D array, e.g. ARRAY[1:3, 1:3] OF CHAR

3. A program stores the marks of 30 students over 4 tests. Which array fits best?

A One 1D array: ARRAY[1:30] OF INTEGER

B One 2D array: ARRAY[1:30, 1:4] OF INTEGER

4. Which statement about choosing an array is correct?

A Use a 2D array when each value needs a row and a column to locate it

B Use a 2D array whenever you have more than 10 values

5. Which array would you use to find a student's mark with Marks[5, 2]?

A A 2D array, because two indexes are used

B A 1D array, because it is a list of marks

Match the Pairs

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

Left column		Right column
1DECLARE Names : ARRAY[1:30] OF STRING		AThe array is 1D but is used with two indexes. Marks for students and tests form a table, so it should be declared as 2D: ARRAY[1:30, 1:4] OF INTEGER.
2DECLARE Board : ARRAY[1:3, 1:3] OF CHAR		BA 1D array: one simple list of 30 names, where each name is found using a single index
3Marks for 30 students over 4 tests form a table, so each mark needs a student (row) and a test (column)		CNames[5] <- "Ava" Scores[5] <- 88
4Parallel 1D arrays store related lists side by side, and the same index links the matching items		DDECLARE Marks : ARRAY[1:30, 1:4] OF INTEGER
5DECLARE Marks : ARRAY[1:120] OF INTEGER Marks[3, 2] <- 75		EA simple list of names needs only one index, so a 2D array is unnecessary. It should be DECLARE Names : ARRAY[1:30] OF STRING and Names[7] <- "Zoe".
6DECLARE Names : ARRAY[1:30, 1:1] OF STRING Names[7, 1] <- "Zoe"		FA 2D array: a 3 by 3 game board grid, where each square is found using a row and a column

Definitions

1D or 2D array

Fill in the Blanks

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

DECLARE Names : ARRAY[____] OF STRING

DECLARE Board : ARRAY[1:3, ___] OF CHAR

DECLARE Marks : ARRAY[1:30, ___] OF INTEGER

// mark for each student and test OUTPUT _____[Student, Test]

// parallel 1D arrays share one index OUTPUT Names[I], Marks[_]

Spot the Error

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

Question 1

A Names[5,1] ← "Zoe"

B Names[6] ← "Leo"

C OUTPUT Names[5]

Question 2

A Board[2] ← "X"

B Board[1,3] ← "O"

C OUTPUT Board[2,2]

Question 3

A Marks[1,1] ← 72

B Marks[1,2] ← 65

C Marks[2,1] ← 58

D Marks[2] ← 80

Question 4

A Name[3] ← "Mia"

B Mark[4] ← 91

C OUTPUT Name[3], Mark[3]

Question 5

A FOR r ← 1 TO 3

B FOR r ← 1 TO 3

C Board[r,c] ← "-"

D NEXT c

E NEXT r

Answer Key

Choosing a 1D or 2D array for a scenario

Section A: Quick Questions

A — A 1D array, e.g. ARRAY[1:30] OF STRING

B — A 2D array, e.g. ARRAY[1:3, 1:3] OF CHAR

B — One 2D array: ARRAY[1:30, 1:4] OF INTEGER

A — Use a 2D array when each value needs a row and a column to locate it

A — A 2D array, because two indexes are used

Section B: Match the Pairs

DECLARE Names : ARRAY[1:30] OF STRING → A 1D array: one simple list of 30 names, where each name is found using a single index

DECLARE Board : ARRAY[1:3, 1:3] OF CHAR → A 2D array: a 3 by 3 game board grid, where each square is found using a row and a column

Marks for 30 students over 4 tests form a table, so each mark needs a student (row) and a test (column) → DECLARE Marks : ARRAY[1:30, 1:4] OF INTEGER

Parallel 1D arrays store related lists side by side, and the same index links the matching items → Names[5] <- "Ava" Scores[5] <- 88

DECLARE Marks : ARRAY[1:120] OF INTEGER Marks[3, 2] <- 75 → The array is 1D but is used with two indexes. Marks for students and tests form a table, so it should be declared as 2D: ARRAY[1:30, 1:4] OF INTEGER.

DECLARE Names : ARRAY[1:30, 1:1] OF STRING Names[7, 1] <- "Zoe" → A simple list of names needs only one index, so a 2D array is unnecessary. It should be DECLARE Names : ARRAY[1:30] OF STRING and Names[7] <- "Zoe".

Section C: Definitions

1D or 2D array — Use a 1D array for a simple list of values. Use a 2D array when data forms a table or grid, so each value needs two indexes: a row and a column.

Section D: Fill in the Blanks

DECLARE Names : ARRAY[1:30] OF STRING

DECLARE Board : ARRAY[1:3, 1:3] OF CHAR

DECLARE Marks : ARRAY[1:30, 1:4] OF INTEGER

// mark for each student and test
OUTPUT Marks[Student, Test]

// parallel 1D arrays share one index
OUTPUT Names[I], Marks[I]

Section E: Spot the Error

A — A list of 30 names is a 1D array, so each name needs only one index. It should be Names[5] ← "Zoe".

A — A game board is a grid, so it is a 2D array and each square needs a row and a column. It should be Board[2,2] ← "X".

D — Marks for students across several tests form a table, so a 2D array. You need the student (row) and the test (column): Marks[2,2] ← 80.

B — With parallel 1D arrays, the same index must be used for the same student. Mia is at index 3 in Name, so her mark must be Mark[3] ← 91.

B — A 2D board needs two different loop variables, one for rows and one for columns. The inner loop should be FOR c ← 1 TO 3, because Board[r,c] uses c.