2.4a Data Structures — Edexcel 1CP2

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⭐ Enrichment lesson — this topic is not assessed in the Edexcel 1CP2 GCSE exam. It provides valuable extra knowledge but should not replace revision of the core specification.

What is a Data Structure?

A data structure is an organised way of storing and managing data so it can be accessed and modified efficiently. Edexcel 1CP2 requires knowledge of arrays and records.

Arrays

An array is an ordered collection of elements of the same data type, stored in consecutive memory locations. Arrays have a fixed size (in most languages).

1D Arrays

A 1D array (single list) is like a row of boxes, each with an index number.

Index	0	1	2	3	4
Value	"Ali"	"Beth"	"Carl"	"Dana"	"Eve"

names[0] returns "Ali" · names[3] returns "Dana" (zero-indexed)

Access any element in O(1) time using its index
Useful for storing a list of the same type (scores, names, temperatures)
In Edexcel pseudocode: names = ["Ali","Beth","Carl","Dana","Eve"]

2D Arrays

A 2D array is an array of arrays — like a table with rows and columns. Used for grids, matrices, and seating plans.

	Col 0	Col 1	Col 2
Row 0	10	20	30
Row 1	40	50	60

grid[1][2] returns 60 (row 1, column 2)

Access element with two indices: array[row][col]
Useful for: game boards, spreadsheets, images (pixels), seating arrangements

Records

A record is a data structure that groups together related data items of different data types under one name. Think of it like a row in a database table.

Field	name	age	height	isMember
Data type	String	Integer	Real	Boolean
Example value	"Ali"	16	1.72	TRUE

In Edexcel pseudocode:

RECORD Student
  name : STRING
  age : INTEGER
  height : REAL
ENDRECORD

Arrays vs Records

Feature	Array	Record
Data types	All the same	Can be mixed (different fields)
Access	By index number	By field name
Use case	List of similar items	Single entity with multiple attributes
Example	List of 30 test scores	One student's name, age, score

Exam tip: Know the difference: arrays store the same data type; records store different data types in named fields. A common Edexcel question asks you to choose which is most appropriate for a given scenario — e.g. "storing the name, age and score of one pupil" → record; "storing 30 test scores" → 1D array.

⚠️ Common Mistakes

Using index 1 instead of 0 — arrays in most languages are zero-indexed
Saying arrays can store different data types — they can't (that's a record)
Confusing 2D array notation: grid[row][col] not grid[col][row]

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Worksheet — 2.4a Data Structures

8 questions · Arrays & Records

Q1Define the term 'array' in programming.[2]

✅ Mark scheme

An array is a data structure that stores an ordered collection of elements [1]; all of the same data type, accessed by index [1].

Q2A 1D array called scores contains: [45, 72, 88, 91, 55]. What is the value of scores[3]?[1]

✅ Mark scheme

91 [1] (zero-indexed: index 3 is the fourth element).

Q3What is a 2D array? Give ONE example of when a 2D array would be appropriate.[3]

✅ Mark scheme

A 2D array is an array of arrays, forming a table with rows and columns [2]; example: seating plan, noughts and crosses grid, spreadsheet data, image pixel values [1].

Q4A 2D array called grid is: [[1,2,3],[4,5,6],[7,8,9]]. What is grid[2][1]?[1]

✅ Mark scheme

8 [1] (row 2 = [7,8,9]; column 1 = 8).

Q5What is a record? How does it differ from an array?[3]

✅ Mark scheme

A record is a data structure that groups related data items under one name [1]; records can store different data types in named fields [1]; arrays can only store elements of the same data type, accessed by index [1].

Q6A school database stores student information: name, age, year group, and whether they have a bus pass. Should this be stored in an array or a record? Justify your answer.[3]

✅ Mark scheme

A record [1]; because the fields have different data types: name (String), age (Integer), year group (Integer), bus pass (Boolean) [1]; records store different data types in named fields, whereas arrays only store one data type [1].

Q7Write pseudocode to declare a 1D array called temperatures containing five values: 21.3, 19.8, 22.5, 18.0, 20.1[2]

✅ Mark scheme

temperatures = [21.3, 19.8, 22.5, 18.0, 20.1] [2]; or equivalent array declaration syntax showing 5 real/float values [2].

Q8State ONE advantage of using an array over separate variables to store a list of 100 test scores.[2]

✅ Mark scheme

Any one: all values stored under one name with a single index [1]; can use a loop to process all 100 values without repeating code 100 times [1]; easier to add/remove values [1].

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What is a Data Structure?

Arrays

1D Arrays

2D Arrays

Records

Arrays vs Records

Worksheet — 2.4a Data Structures

Mini Test — Data Structures