Software Design and Development

Detecting and correcting errors- answers

Activity 1

The five errors are corrected and explained in red:

Private Sub cmdSkillsTest_Click()	' Math skills test
Dim lngBefore As Long Dim lngAfter As Long Dim lngTimeDiff As Long Dim strAns As String Dim intResult As Integer lngBefore = Timer Do	‘Missing keyword in grouping ‘VB variables cannot start with ‘digit (2time) ' Save seconds since midnight
strAns = InputBox("What is 150 + 235?","Hurry”)	‘Missing‘ punctuation
Loop Until Val(strAns) = 385 lngAfter = Timer	‘Typing mistake in reserved word ' Save seconds since midnight
‘The difference between the stored time values is how many seconds the user took to answer the question.
lngTimeDiff = lngAfter – lngBefore ‘Variable name typing error intResult = MsgBox ("That took you only "& Str(lngTimeDiff) & " seconds!")
End Sub

Congratulations if you found all five errors! You have sharp eyes.

Activity 1 PHP Answer

CODE	Error	Fixed code
Ehco “Hello there”;	Spelling of function	Echo “Hello there”;
IF ($age < 13){ Echo “Child” }	1 error Missing semi-colon ; that end each line of code	IF ($age < 13){ Echo “Child”; }
IFS (age < 13){ Echo “Child”; }	2 errors Key work IF miss-spelt Variable age must have a $	IF ($age < 13){ Echo “Child”; }
$count = 0; WHILE count < 10 $count = $count + 1; Echo “count “; }	2 errors Condition of the loop must be within brackets ( ) Curly brackets missing	$count = 0; WHILE (count < 10){ $count = $count + 1; Echo “$count “; }

Activity 2

The hand trace shows the value stored in number has gone to –1 without ever becoming zero. An endless loop has beencreated.

Activity 2 PHP answer

The following algorithms print out the numbers 1 to 5
(Expected output is 1, 2, 3, 4, 5)

Code	Output	Explain and fix the error
$count = 0; WHILE ($count < 3) { $count = $count + 1; Echo “ $count”; }	1 2 3	Loop only executed 3 times, change condition to count < 5
$count = 0; WHILE ($count < 5) { Echo “ $count; }	0 0 0 0 ... endless loop	Endless loop as the variable count is not incremented within the loop Add count = count + 1
$index = 0; WHILE ($index < 5) { $count = $count + 1; Echo “ $count”; }	0 0 0 0 ...endless loop	Variable names change. Change all index to count
$count = 0; WHILE ($count < 5) { Echo “ $count }	0 1 2 3 4	Variable is ouputted before be incremeted. Either set count to 1, or move count=count+1 to above ECHO
$count = 0; WHILE ($count < 5) { $count = $count - 1; Echo “ $count”; }	-1 -2 -3 ...endless loop	Varible is incremented incorrectly. Change to $count=$count+1

The following code calculates the average of 2 numbers
(test data, enter 6, 4 should display 5)

Code	Output	Explain and fix the error
$average = $num1 + $num2 / 2; Echo “The average is”; $average”;	8	Average=6 + 4/2
Echo "The average is"; $average";		Average = 6 + 2 2 values are not added before dividing by 2 Add brackets $average = ($num1 + $num2) / 2;

The following algorithms print out if someone is able to legally vote

Code	Explain and fix the error
IF ($age > 18) { Echo “Legal”; }ELSE{ Echo “Not legal”; }	When age=18, Not legal is incorrectly displayed. Change condition to ($age >= 18)

Activity 3

Desk checking the original algorithm with a value like 4 (sum = 4+3+2+1 = 10) should have revealed the error. This code gives a sum of 6.

The hand execution results are shown below.

The problem is fixed by placing the line number = number - 1 after the sum = sum + number line.

Loop iteration	number	sum	expected sum
0	4	0
1	3	3	4
2	2	5	7
3	1	6	9
4	0	6	10

Activity 4 PHP answer

Code	Output	Explain and fix the error
$count = 0; WHILE ($count < 5) { Echo “ $count”; }	0 0 0 0 ...endless loop	The endless loop could cause an overflow error if $count is set as an integer where there is a limit ti the value it can hold. Add $count = $count + 1 to increment the count.