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Testing an algorithm
When an algorithm is created it needs to be tested and checked to see if it works. There are two common methods used to test an algorithm:
- Desk-checking
- Walk-through
It is best to get someone else to check your algorithm, this is called peer checking. (If you wrote the algorithm you are less likely to spot the mistakes).
Desk-checking
Involves drawing up a table of the variables and outputs from the algorithm and then methodically working through the algorithm, with sets of test data, recording the changing values of the variables. The final results can then be compared to the expected results to see if the algorithm works as it should.
Example
The following algorithm is meant to calculate the average of 5 numbers. So for the test data, of 5, 4, 6, 2, 8 the average should be (25/5 = 5)
BEGIN
Count = 0
Total = 0
Average = 0
REPEAT
Count = count + 1
Get number
Total = Total + number
UNTIL count = 5
Average = Total/Count
Display average
END
| Count | Total | Number | Average | Output |
|---|---|---|---|---|
| 0 | 0 | 0 | ||
| 1 | 5 | 5 | ||
| 2 | 9 | 4 | ||
| 3 | 15 | 6 | ||
| 4 | 17 | 2 | ||
| 5 | 25 | 8 | 5 | 5 |
Activity 1:
The following algorithm is meant to work out the pay for an employee, given the payrate and number of hours they have worked each day.
BEGIN
count = 0
Totalhours = 0
Enter Payrate
WHILE count < 7
count=count + 1
Enter hours worked
Totalhours = Totalhours + hours
END WHILE
Pay = payrate * Totalhours
Display Pay
END
Complete a desk check, using the following test data:
- Payrate = $10.00, hours = 4, 2, 0, 8, 0, 0, 4
- (Expected output is 10.00 * 18 = 180.00)
| Variables | Outputs | ||||
|---|---|---|---|---|---|
| Count | Hours | Totalhours | Payrate | Pay | |
Check your Answer
Walk-through
A walk-through is used to quickly test the logic of an algorithm or to find out what an algorithm does. It is usually done mentally and this is what a peer-checker might do to check the logic of the algorithm.
Activity 2:
Outline examples of errors you might expect to find using a Walk-through.
Check your Answer
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