Code Guide: Nested Selection Programs With Multiple Conditions (Copy)

Nested Selection Programs With Multiple Conditions

What Nested Selection Means

• Nested selection is when an IF statement is placed inside another IF / ELSE block
• Used when:
  • The second decision depends on the first decision being true (or false)
  • You need to apply multiple rules in layers
• Typical exam wording that signals nesting:
  • “If … then check whether …”
  • “Only if …, then …”
  • “If eligible, then decide which type…”

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When To Use Nested IF (Vs ELSE IF Chains)

Situation	Best Structure	Why
Second decision only matters after first is TRUE	Nested IF	Cleaner + matches wording
Multiple independent ranges (grades, bands)	ELSE IF chain	Ordered conditions are clearer
Validation + categorisation	Nested IF	First validate, then categorise
Two separate factors both matter (e.g., age + membership)	Nested IF	Layered logic is natural

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Core Rules (Exam-Critical)

• A nested IF must be:
  • Correctly indented
  • Clearly inside the correct branch
  • Logically reachable
• Conditions must be:
  • Non-overlapping (or ordered properly)
  • Reachable
  • Written using correct AND / OR
• Always think:
  • “What must be true for the inner IF to even run?”

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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 AS Level Computer Science Full Scale Course

Pattern 1: Eligibility Check Then Category (Most Common Exam Pattern)

Scenario

• A person is eligible only if age ≥ 18
• If eligible, check whether they are a senior (age ≥ 60)

Pseudocode

INPUT age

IF age >= 18 THEN
  OUTPUT "Eligible"
  IF age >= 60 THEN
    OUTPUT "Senior Eligible"
  ELSE
    OUTPUT "Adult Eligible"
  ENDIF
ELSE
  OUTPUT "Not Eligible"
ENDIF

Why This Is Nested (And Correct)

• The “senior vs adult” decision only makes sense if the person is already eligible

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Pattern 2: Validation Then Processing (High Mark Saver)

Scenario

• Input mark (must be 0 to 100)
• If valid, assign grade
• If invalid, output error

Pseudocode

INPUT mark

IF mark >= 0 AND mark <= 100 THEN
  IF mark >= 80 THEN
    OUTPUT "A"
  ELSEIF mark >= 65 THEN
    OUTPUT "B"
  ELSEIF mark >= 50 THEN
    OUTPUT "C"
  ELSE
    OUTPUT "F"
  ENDIF
ELSE
  OUTPUT "Invalid Mark"
ENDIF

Why This Scores Well

• Outer IF protects the grading logic
• Inner chain handles categorisation only after validation

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Pattern 3: Two-Factor Decision (Membership + Spending)

Scenario

• Discount depends on:
  • Membership status
  • Total bill value

Pseudocode

INPUT member
INPUT bill

IF member = TRUE THEN
  IF bill >= 5000 THEN
    discount ← bill * 0.20
  ELSE
    discount ← bill * 0.10
  ENDIF
ELSE
  IF bill >= 5000 THEN
    discount ← bill * 0.05
  ELSE
    discount ← 0
  ENDIF
ENDIF

finalBill ← bill - discount
OUTPUT finalBill

Exam Takeaway

• Nested selection handles combinations cleanly without messy multi-condition IF lines

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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 AS Level Computer Science Full Scale Course

Pattern 4: Multiple Conditions Inside One Decision (AND / OR Inside Nested IF)

Scenario

• User can login only if username is correct
• If username correct, password must be correct AND account must be active

Pseudocode

INPUT username
INPUT password
INPUT active

IF username = "admin" THEN
  IF password = "1234" AND active = TRUE THEN
    OUTPUT "Login Success"
  ELSE
    OUTPUT "Login Failed"
  ENDIF
ELSE
  OUTPUT "Unknown User"
ENDIF

Key Rule

• Put the most “gating” check first (username)
• Only then check more detailed conditions (password + active)

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Pattern 5: Avoiding Impossible Conditions Using Nesting

Common Student Mistake (Bad Logic)

• Trying to force everything into one condition:
  • IF age >= 18 AND age < 13 THEN (impossible)

Correct Nested Logic

• First decide age band, then sub-band:

INPUT age

IF age < 13 THEN
  OUTPUT "Child"
ELSE
  IF age < 20 THEN
    OUTPUT "Teen"
  ELSE
    OUTPUT "Adult"
  ENDIF
ENDIF

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Pattern 6: Nested Selection With Flags (Common With Search / Detection)

Scenario

• Scan 10 inputs
• If any value is negative, set error flag
• If error flag TRUE, decide severity

Pseudocode

error ← FALSE

FOR i ← 1 TO 10
  INPUT num
  IF num < 0 THEN
    error ← TRUE
  ENDIF
NEXT i

IF error = TRUE THEN
  INPUT critical
  IF critical = TRUE THEN
    OUTPUT "Critical Error"
  ELSE
    OUTPUT "Minor Error"
  ENDIF
ELSE
  OUTPUT "No Error"
ENDIF

Why Nested

• The severity check only runs if an error exists

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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 AS Level Computer Science Full Scale Course

Nested Selection Templates (Copy-Paste Safe)

Template A: Eligibility Then Category

IF eligibleCondition THEN
  IF categoryCondition THEN
    OUTPUT "Category 1"
  ELSE
    OUTPUT "Category 2"
  ENDIF
ELSE
  OUTPUT "Not Eligible"
ENDIF

Template B: Validation Then Processing

IF validCondition THEN
  IF mainCondition THEN
    OUTPUT "Case 1"
  ELSEIF otherCondition THEN
    OUTPUT "Case 2"
  ELSE
    OUTPUT "Case 3"
  ENDIF
ELSE
  OUTPUT "Invalid Input"
ENDIF

Template C: Two-Factor Combination (4 outcomes)

IF factorA THEN
  IF factorB THEN
    OUTPUT "A and B"
  ELSE
    OUTPUT "A only"
  ENDIF
ELSE
  IF factorB THEN
    OUTPUT "B only"
  ELSE
    OUTPUT "Neither"
  ENDIF
ENDIF

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Trace Table Practice (Nested IF)

Pseudocode

INPUT age

IF age >= 18 THEN
  IF age >= 60 THEN
    OUTPUT "Senior"
  ELSE
    OUTPUT "Adult"
  ENDIF
ELSE
  OUTPUT "Minor"
ENDIF

Test Values + Outputs

age	Outer IF (age >= 18)	Inner IF (age >= 60)	Output
12	FALSE	—	Minor
30	TRUE	FALSE	Adult
70	TRUE	TRUE	Senior

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Common Examiner-Reported Mistakes (And Fixes)

Mistake 1: Wrong Nesting Location

• Bug pattern:
  • Inner IF accidentally placed outside outer IF
• Fix:
  • Ensure inner IF is indented and inside the correct branch

Mistake 2: Unreachable Inner Conditions

• Example:
  • Outer IF: mark >= 80
  • Inner IF: mark >= 50 (always true inside outer)
• Fix:
  • Inner checks must add new information, not repeat weaker conditions

Mistake 3: ELSE IF Ordering Incorrect

• Example (wrong order):
  • Check mark >= 50 before mark >= 80
• Fix:
  • Order from highest threshold to lowest

Mistake 4: Wrong AND / OR

• Invalid range check:
  • mark < 0 AND mark > 100
• Correct:
  • Invalid condition uses OR
  • Valid condition uses AND:
    • mark >= 0 AND mark <= 100

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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 AS Level Computer Science Full Scale Course

High-Yield Practice Mini Programs (Nested, Multi-Condition)

Program 1: Shipping Cost Based On Weight And Location

INPUT weight
INPUT international

IF weight <= 0 THEN
  OUTPUT "Invalid Weight"
ELSE
  IF international = TRUE THEN
    IF weight <= 5 THEN
      cost ← 2000
    ELSE
      cost ← 4000
    ENDIF
  ELSE
    IF weight <= 5 THEN
      cost ← 800
    ELSE
      cost ← 1500
    ENDIF
  ENDIF
  OUTPUT cost
ENDIF

Program 2: Exam Result With Distinction Rule

• Pass mark: 50
• Distinction: 80+
• If invalid mark, output error

INPUT mark

IF mark >= 0 AND mark <= 100 THEN
  IF mark >= 80 THEN
    OUTPUT "Distinction"
  ELSE
    IF mark >= 50 THEN
      OUTPUT "Pass"
    ELSE
      OUTPUT "Fail"
    ENDIF
  ENDIF
ELSE
  OUTPUT "Invalid Mark"
ENDIF

Program 3: Username Check Then Role-Based Access

INPUT username
INPUT role

IF username = "admin" THEN
  IF role = "A" THEN
    OUTPUT "Full Access"
  ELSEIF role = "B" THEN
    OUTPUT "Limited Access"
  ELSE
    OUTPUT "No Access"
  ENDIF
ELSE
  OUTPUT "Unknown User"
ENDIF

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Final Checklist Before Writing Nested Selection In Exams

• Did you choose nesting because the inner decision depends on the outer decision?
• Are all conditions reachable and ordered correctly?
• Did you avoid impossible conditions?
• Did you cover all outcomes with ELSE where needed?
• Is indentation clean and unambiguous?

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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 AS Level Computer Science Full Scale Course