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c. Practical Examples

Example 1: Using a breakpoint to trace a logic error

A module is designed to calculate the total cost of items purchased.

Intended logic 

totalCost ← quantity * price

Observed problem

When quantity = 3 and price = 10, the output produced is 0.

How a breakpoint helps

A breakpoint is placed on the line:

totalCost ← quantity * price

When execution pauses:

  • quantity = 0
  • price = 10

This shows that:

  • The variable quantity has not been assigned correctly before the calculation
  • The error occurs before the calculation line

Conclusion

The breakpoint allows the developer to inspect variable values at runtime and identify where program logic fails.

Example 2: Using debugging statements to track program flow

A developer suspects that a decision structure is not executing as intended.

Code with debugging statements 

Print "Start calculation"

If score ≥ 50 then
    Print "Pass condition met"
    result ← "Pass"
Else
    Print "Fail condition met"
    result ← "Fail"
End If

Program output 

Start calculation
Fail condition met

Given that score = 65, this output indicates:

  • The condition is being evaluated incorrectly
  • The wrong branch of the decision structure is executing

Conclusion

Debugging statements confirm which parts of the code are running and help locate logic errors.

Example 3: Constructing relevant test data

A module only accepts values between 1 and 100 inclusive.

Appropriate test data

Type Values
Valid 1, 50, 100
Boundary 1, 100
Invalid 0, 101

Using this range ensures:

  • Normal operation is tested
  • Edge cases are tested
  • Error handling is tested

Example 4: Testing table – expected vs actual output

A module calculates the square of a number.

Testing table

Test data Expected output Actual output Pass / Fail
5 25 25 Pass
0 0 0 Pass
-3 Error message 9 Fail

Interpretation

  • The module correctly handles valid data
  • The module does not handle invalid data correctly
  • Debugging is required to correct how negative values are processed

Example 5: Linking testing and debugging

  1. Testing identifies that the output does not match expectations
  2. A testing table records the discrepancy
  3. Debugging techniques (breakpoints or debugging statements) are used
  4. The error is corrected
  5. The test is re-run to confirm the fix

This cycle continues until all tests pass.

40+ Exam Insight

Important

Testing tables do not fix errors.

They provide evidence that an error exists and justify the need for debugging.