Arrays, Records & Data Handling: Updating Array Values Based On Conditions (Copy)

Updating Array Values Based On Conditions (Cambridge Standard – O Level 2210 + IGCSE 0478)

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Why Conditional Array Updates Are Heavily Tested In Paper 2

• Updating array values based on conditions is used to:
  • Modify stored data safely
  • Apply rules to existing records
  • Correct, adjust, or normalise values
• Cambridge tests this to assess:
  • Correct traversal logic
  • Accurate condition placement
  • Safe in-place updates without breaking bounds
• This pattern appears frequently in:
  • Pre-release material algorithms
  • Section B modification tasks
  • Pseudocode completion questions

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Core Concept: Conditional Update Vs Conditional Processing

• Conditional processing:
  • Uses IF to decide what to count, output, or total
• Conditional updating:
  • Uses IF to decide what value in the array should change

Key distinction:

• The array element itself is modified

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Fundamental Pattern For Conditional Updates

Standard Cambridge-Safe Pattern

• FOR index ← lowerBound TO upperBound
  • IF condition(arrayName[index]) THEN
    • arrayName[index] ← newValue
  • ENDIF
• ENDFOR

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Examiner Expectations

• Loop traverses full required range
• IF condition is evaluated per element
• Assignment updates the array element directly
• No modification of loop index

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Simple Conditional Update Examples

Example 1: Resetting Invalid Values

• FOR i ← 1 TO 30
  • IF marks[i] < 0 OR marks[i] > 100 THEN
    • marks[i] ← 0
  • ENDIF
• ENDFOR

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Example 2: Applying Bonus Marks

• FOR i ← 1 TO 30
  • IF marks[i] >= 40 AND marks[i] < 50 THEN
    • marks[i] ← marks[i] + 5
  • ENDIF
• ENDFOR

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Examiner Focus

• Update uses:
  • marks[i] on both sides of assignment
• Condition is precise
• No accidental double updates

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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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Updating Arrays While Preserving Valid Data

Safe Update Pattern With Range Protection

• FOR i ← 1 TO 30
  • IF marks[i] >= 0 AND marks[i] <= 100 THEN
    • marks[i] ← marks[i] * 1.05
  • ENDIF
• ENDFOR

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Examiner Expectation

• Validity check before update
• No update to invalid values
• Mathematical operation applied correctly

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Conditional Update With ELSE Clause

Two-Way Update Pattern

• FOR i ← 1 TO 20
  • IF attendance[i] = TRUE THEN
    • points[i] ← points[i] + 2
  • ELSE
    • points[i] ← points[i] + 0
  • ENDIF
• ENDFOR

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Examiner Note

• ELSE is optional
• Use ELSE only when:
  • Both outcomes require explicit action

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Conditional Update Using Nested Selection

Multi-Condition Update

• FOR i ← 1 TO 30
  • IF marks[i] >= 80 THEN
    • grade[i] ← “A”
  • ELSEIF marks[i] >= 65 THEN
    • grade[i] ← “B”
  • ELSEIF marks[i] >= 50 THEN
    • grade[i] ← “C”
  • ELSE
    • grade[i] ← “F”
  • ENDIF
• ENDFOR

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Examiner Expectations

• Conditions ordered correctly (highest to lowest)
• Exactly one update per element
• No overlapping conditions

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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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Updating Arrays Based On Another Array

Cross-Array Conditional Update

• FOR i ← 1 TO 30
  • IF valid[i] = TRUE THEN
    • marks[i] ← marks[i] + bonus
  • ENDIF
• ENDFOR

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Examiner Focus

• Index used consistently across arrays
• Both arrays share same bounds
• No mismatched indices

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Updating Arrays Using WHILE Loops

WHILE-Based Update (Allowed, Higher Risk)

• index ← 1
• WHILE index <= 30 DO
  • IF marks[index] < 0 THEN
    • marks[index] ← 0
  • ENDIF
  • index ← index + 1
• ENDWHILE

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Examiner Focus

• index initialised before loop
• index incremented inside loop
• Correct loop termination

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Updating Arrays In Reverse Order

Reverse Update Pattern

• FOR i ← upperBound TO lowerBound STEP -1
  • IF values[i] = 0 THEN
    • values[i] ← defaultValue
  • ENDIF
• ENDFOR

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Examiner Expectation

• STEP is negative
• Bounds respected
• Reverse order justified by task

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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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Updating Two-Dimensional Arrays Based On Conditions

Standard Nested Loop Update Pattern

• FOR r ← rowLower TO rowUpper
  • FOR c ← columnLower TO columnUpper
    • IF data[r,c] < 0 THEN
      • data[r,c] ← 0
    • ENDIF
  • ENDFOR
• ENDFOR

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Examiner Focus

• Nested loops mandatory
• Correct row–column order
• Update applied per cell

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Updating Arrays Without Breaking Trace Logic

• Updates affect:
  • Subsequent operations
• Trace tables must:
  • Reflect updated values
• Do not:
  • Assume original values persist after update

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Trace Table Implication Example

• IF marks[i] < 0 THEN
  • marks[i] ← 0
• Next iteration using marks[i]:
  • Uses updated value

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Common Conditional Update Errors (Guaranteed Mark Loss)

• Updating loop index instead of array element
• Using wrong index variable
• Updating outside array bounds
• Multiple updates per iteration unintentionally
• Forgetting ENDIF
• Using assignment operator incorrectly

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High-Risk Mistake Example

• IF marks[i] < 50 THEN
  • i ← i + 1
• This modifies loop control variable
• Guaranteed logical failure

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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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Conditional Updates In Pre-Release Material

• Pre-release tasks often require:
  • Normalising values
  • Applying penalties or bonuses
  • Correcting invalid data
• You must:
  • Follow rules exactly as stated
  • Not invent extra conditions
  • Not update values outside specification

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Conditional Updates In Section B Modifications

• Section B frequently asks:
  • “Modify the algorithm so that…”
• Safe strategy:
  • Insert IF inside existing loop
  • Update array element directly
  • Do not alter loop bounds or declaration

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Example Section B 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
    • marks[i] ← marks[i] + 2
    • total ← total + marks[i]
  • ENDIF
• ENDFOR

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Examiner Checklist For Safe Conditional Updates

• Loop bounds match array declaration
• IF condition is precise and complete
• Only array element is updated
• Loop index untouched
• Update does not cause out-of-range values
• Logic remains traceable

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Best-Practice Strategy For Paper 2

• Decide clearly:
  • What condition triggers update
  • What new value should be assigned
• Use FOR loops for full traversal
• Use WHILE only when necessary
• Combine update and accumulation carefully
• Trace one full iteration manually

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Final Quality Checklist

• Correct loop structure
• Correct condition placement
• Correct assignment target
• No boundary violations
• No loop variable modification
• Updated values used consistently

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Final Lock-In Rules

• Conditional updates modify array contents
• IF controls whether update occurs
• Loop controls how many elements are checked
• Loop index must never be modified
• Clean conditional updates = safe Paper 2 marks

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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