Arrays, Records & Data Handling: One-Dimensional Array Declaration And Indexing (Copy)

One-Dimensional Array Declaration And Indexing (Cambridge Standard – O Level 2210 + IGCSE 0478)

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Purpose Of One-Dimensional Arrays In Cambridge Pseudocode

• One-dimensional arrays are used to:
  • Store multiple values of the same data type
  • Allow efficient processing using loops
• Cambridge tests arrays to assess:
  • Correct declaration
  • Safe indexing
  • Integration with loops, selection, procedures, and functions
• Arrays are central to:
  • Pre-release material
  • Section B modifications
  • Trace table questions

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What Cambridge Means By A One-Dimensional Array

• A one-dimensional array is:
  • A list of values
  • Stored under a single variable name
  • Accessed using an index
• All elements:
  • Must be of the same data type
• Index:
  • Identifies the position of each element

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Core Array Declaration Structure (Cambridge Standard)

• DECLARE arrayName[lowerBound:upperBound] : dataType

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Key Declaration Rules

• DECLARE keyword is mandatory
• arrayName:
  • Must be meaningful
• lowerBound and upperBound:
  • Define valid index range
• dataType:
  • Must match stored values

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Example Declarations

• DECLARE marks[1:30] : INTEGER
• DECLARE names[1:20] : STRING
• DECLARE prices[0:9] : REAL
• DECLARE present[1:50] : BOOLEAN

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Indexing System Used By Cambridge

• Cambridge allows:
  • Any valid lower bound (0 or 1 most common)
• The index range is:
  • Explicitly defined in the declaration
• Indexing is:
  • Inclusive of both bounds

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Example Index Ranges

Declaration	Valid Index Values
marks[1:5]	1, 2, 3, 4, 5
data[0:9]	0 to 9
scores[5:10]	5 to 10

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Examiner Focus

• Loop boundaries must:
  • Match array bounds exactly
• Any mismatch:
  • Leads to out-of-range access
  • Causes mark loss

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Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Computer Science Full Scale Course

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Accessing Array Elements (Indexing Syntax)

Standard Access Format

• arrayName[index]

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Examples

• marks[1]
• names[i]
• prices[count]

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Assignment To Array Elements

• marks[3] ← 75
• names[1] ← “Ali”

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Reading From Array Elements

• total ← total + marks[i]
• OUTPUT names[index]

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Using Arrays With FOR Loops (Most Tested Pattern)

Standard Traversal Pattern

• FOR i ← lowerBound TO upperBound
  • PROCESS arrayName[i]
• ENDFOR

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Example

• total ← 0
• FOR i ← 1 TO 30
  • total ← total + marks[i]
• ENDFOR

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Examiner Expectations

• Loop variable:
  • Matches array index type
• Loop boundaries:
  • Match declared bounds
• No hardcoded values if bounds are known

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Common Array Indexing Errors (High-Risk)

Error 1: Out-Of-Bounds Index

• Accessing marks[31] when declared [1:30]

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Error 2: Incorrect Loop Start Or End

• FOR i ← 0 TO 29
  • marks[i]
• ENDFOR
• Invalid if array declared [1:30]

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Error 3: Using Wrong Index Variable

• FOR i ← 1 TO 10
  • total ← total + marks[j]
• ENDFOR
• j not controlled by loop

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Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Computer Science Full Scale Course

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Inputting Values Into One-Dimensional Arrays

Standard Input Pattern

• FOR i ← lowerBound TO upperBound
  • INPUT arrayName[i]
• ENDFOR

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Example

• FOR i ← 1 TO 20
  • INPUT names[i]
• ENDFOR

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Examiner Expectations

• INPUT occurs inside loop
• One value per iteration
• Array filled sequentially

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Outputting Values From Arrays

Standard Output Pattern

• FOR i ← lowerBound TO upperBound
  • OUTPUT arrayName[i]
• ENDFOR

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Example

• FOR i ← 1 TO 10
  • OUTPUT marks[i]
• ENDFOR

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Arrays And Selection Logic

Conditional Processing Of Arrays

• FOR i ← 1 TO 30
  • IF marks[i] >= 50 THEN
    • passCount ← passCount + 1
  • ENDIF
• ENDFOR

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Examiner Focus

• Selection does not control iteration
• Loop runs full range
• IF filters processing

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Arrays And Accumulators

Correct Accumulator Use

• sum ← 0
• FOR i ← 1 TO n
  • sum ← sum + values[i]
• ENDFOR

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Common Accumulator Errors

• Initialising accumulator inside loop
• Using array index incorrectly
• Forgetting to initialise accumulator

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Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Computer Science Full Scale Course

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Arrays And Trace Tables

How Arrays Appear In Trace Questions

• Trace tables often include:
  • Index variable
  • Current array element
  • Updated accumulators or counters

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Trace Example Concept

• FOR i ← 1 TO 3
  • total ← total + marks[i]
• ENDFOR

Trace variables:

• i
• marks[i]
• total

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Common Trace Errors

• Skipping first element
• Stopping one iteration early
• Using incorrect index values

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Arrays In Pre-Release Material

• Pre-release tasks frequently:
  • Store data in arrays
  • Process arrays using loops
• You must:
  • Respect declared array size
  • Never exceed bounds
  • Use correct index variable

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Arrays In Section B Modifications

• Section B commonly asks to:
  • Add validation to array input
  • Process subset of array
  • Ignore invalid entries
• Safe strategy:
  • Add IF inside loop
  • Do not change array bounds

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Example Modification

Original:

• FOR i ← 1 TO 30
  • total ← total + marks[i]
• ENDFOR

Modified:

• FOR i ← 1 TO 30
  • IF marks[i] >= 0 AND marks[i] <= 100 THEN
    • total ← total + marks[i]
  • ENDIF
• ENDFOR

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Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Computer Science Full Scale Course

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Illegal Array Practices (Guaranteed Mark Loss)

• Accessing out-of-range index
• Using undeclared arrays
• Mixing data types in array
• Modifying loop index manually
• Ignoring declared bounds
• Assuming arrays auto-resize

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Best-Practice Array Strategy For Paper 2

• Declare arrays clearly
• Match loop bounds exactly
• Use meaningful index variables
• Initialise accumulators correctly
• Add selection inside loops when needed
• Respect pre-release constraints

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Final Quality Checklist

• Array declared correctly
• Bounds clearly defined
• Index used safely
• Loop boundaries correct
• No out-of-range access
• Logic traceable

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Final Lock-In Rules

• Arrays store same-type data
• Index range is fixed and inclusive
• Loop boundaries must match array bounds
• Most array errors are boundary errors
• Clean array logic = high Paper 2 accuracy

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Written and Compiled By Sir Hunain Zia (AYLOTI), World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change O Level And IGCSE Computer Science Full Scale Course