← VCE Pseudocode

Binary Search algorithm in pseudocode

An algorithm that repeatedly halves a sorted array to quickly find a target value.

Part of: VCE Pseudo Code — Module 25, VCE Software Development - U3O1 - Programming — Module 148, QCE Digital Solutions Unit 2 — Data and Programming Techniques — Module 119, WA Computer Science ATAR Year 11 — Standard Algorithms — Module 23

Understanding Binary Search algorithm in pseudocode in VCE Pseudocode

What it does: This loop keeps narrowing the range until it's found or exhausted. This condition checks if the middle element matches the target. Binary search only works correctly on a sorted array. Binary search skips half the elements each loop. mid is recalculated from low and high every loop. low and high mark the boundaries of the current range. When low exceeds high, there's no range left to search. This line sets low to the first index of the array.

Common mistakes: Binary search needs sorted data, not unsorted. That's linear search - binary search skips elements.

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This module's key terms are also in a printable crossword (Modules 11–28) and word search (Modules 1–28).

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Learning
Duo
Does binary search require the array to be sorted?
YesNo
Matches
Binary search checks every element
↓
Wrong - it skips half the elements each time
Applying
Meanings
Term
Binary Search
Meaning
An algorithm that repeatedly halves a sorted array to quickly find a target value.
Practice
BEGIN
Testing
Gaps
mid ← (low + high) 2
Check Answer
Spots
1Works on unsorted arrays
2Compares middle element

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Quick Questions

1. Does binary search require the array to be sorted?
A. Yes ✓
B. No
Binary search only works correctly on a sorted array.
2. Does binary search check every element in the array?
A. Yes
B. No ✓
Binary search skips half the elements each loop.
3. Is mid recalculated during each loop?
A. Yes ✓
B. No
mid is recalculated from low and high every loop.
4. Does binary search use low and high to track the search range?
A. Yes ✓
B. No
low and high mark the boundaries of the current range.
5. Is binary search generally faster than linear search on large sorted arrays?
A. No
B. Yes ✓
Halving the range each loop makes binary search much faster.

Match the Pairs

low ← 1 → Sets the starting point of the search range
mid ← (low + high) DIV 2 → Calculates the middle index of the range
Repeatedly halves the search range → WHILE low <= high
Compares the middle element to the target → IF numbers[mid] = target THEN
Binary search checks every element → Wrong - it skips half the elements each time
Binary search works on unsorted arrays → Wrong - the array must be sorted first

Key Term

Binary Search
An algorithm that repeatedly halves a sorted array to quickly find a target value.

Fill in the Blanks

1. mid ← (low + high) DIV 2
Hint: Type the operator used for integer division.
2. WHILE low <= high
Hint: Type the loop keyword that repeats while a condition is true.
3. WHILE low <= high
Hint: Type the comparison operator meaning less than or equal to.
4. IF numbers[mid] = target THEN
Hint: Type the keyword that starts a selection statement.
5. DISPLAY "Found at position", mid
Hint: Type the keyword used to output a message.

Spot the Error

Question 1
A Works on unsorted arrays
B Compares middle element
C Halves the search space
Line A — Binary search needs sorted data, not unsorted.
Question 2
A Data must be sorted first
B Checks every element always
C Uses low, high and mid
Line B — That's linear search - binary search skips elements.
Question 3
A Uses low and high pointers
B mid is the halfway point
C mid never changes value
Line C — mid is recalculated each loop, so it does change.
Question 4
A WHILE low <= high
B mid ← (low + high) DIV 2
C IF numbers[mid] = target
D Loop runs forever always
Line D — The loop stops once low is greater than high.
Question 5
A low starts at 1
B high starts at array size
C mid is halfway between them
D IF numbers[mid] = target THEN
E Search space grows each loop
Line E — The search space shrinks each loop, not grows.

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