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Tracing, debugging, sorting and searching checkpoint

This checkpoint assesses the CT-8 series only. Recall: a trace records changed state in execution order; syntax, runtime and logic errors differ; bubble sort compares adjacent items; binary search requires sorted data and discards half of its remaining range.

Fill in the blanks3 marks

A program that runs but gives an incorrect result has a gap 1 error. Bubble sort compares gap 2 items. Binary search requires a gap 3 structure.

adjacent
logic
sorted
syntax

Multiple choice1 mark

In a trace where blank means unchanged, what does an empty total cell show?

Atotal became zero
Btotal kept its previous value
Ctotal was printed
Dtotal was deleted

Trace table4 marks

Complete the trace table.

Follow the loop and selection in order; record output only when print executes.

Use one row for each pass through the loop. Fill in a box only when that value changes on that row, and leave the rest blank.

ProgramPython

total = 0
for value in [6, 2, 7]:
if value > 4:
total = total + value
print(total)

Trace table with 4 columns
Row	total	value	value > 4	Output
1
2
3
4
5
6

Written answer2 marks

Define a runtime error and give one valid programming example.

Your definition must describe execution, not speed.

Students type their answer here.

Apply bubble sort

Use ascending order and show the state after a complete pass. Remember: compare neighbours from left to right and swap only an out-of-order pair.

Written answer3 marks

Show [9, 4, 7, 2, 6] after one complete ascending bubble-sort pass and state how many comparisons were made.

Record the list after all adjacent comparisons in the pass.

Students type their answer here.

Written answer2 marks

Explain why a complete bubble-sort pass with no swaps is evidence that the list is sorted.

Link every adjacent comparison to order.

Students type their answer here.

Apply binary search

Search only within the current inclusive low to high range. Once a middle item has been checked and is unequal, exclude it when updating the relevant boundary.

Written answer3 marks

Apply binary search to find 38 in [6, 12, 19, 25, 31, 38, 44, 51, 60]. State the compared values in order.

Use integer middle positions.

Students type their answer here.

Multiple choice1 mark

A list changes often and is currently unsorted. Which statement about binary search is correct?

AIt can be applied immediately
BThe list must first be sorted, and that preparation cost matters
CIt compares adjacent pairs
DIt always uses one comparison

Diagnose, amend and retest

The function should return the position of target in a sorted list, or -1 if absent. The upper-bound update contains a logic error.

Coding task4 marks

def binary_position(values, target):
    low = 0
    high = len(values) - 1
    while low <= high:
        middle = (low + high) // 2
        if values[middle] == target:
            return middle
        elif values[middle] < target:
            low = middle + 1
        else:
            high = middle + 1  # fault
    return -1

answer = binary_position([4, 8, 15, 16, 23, 42], 8)
print(answer)

Written answer1 mark

Give one not-found test for binary_position, with its expected result.

Use a sorted list and an absent target.

Students type their answer here.

Route forward

You have secured formal tracing, evidence-led debugging and the two standard algorithms. Later CT series will reuse these methods inside larger programs and testing cycles.