Task 7 Trace Table Practice

Trace tables help you test algorithm logic without guessing. They are especially useful for loops, counters and conditions.

How To Complete A Trace Table

Write the variables as column headings.
Add one row for the starting values.
Step through the algorithm one instruction at a time.
Update a variable only when the algorithm changes it.
Record output only when the algorithm displays something.
Check whether the final result matches what the program should do.

Worked Example

Algorithm:

balancedCount <- 0
FOR session <- 1 TO 3
  INPUT totalMinutes
  IF totalMinutes >= 30 AND totalMinutes <= 60 THEN
    balancedCount <- balancedCount + 1
  ENDIF
ENDFOR
OUTPUT balancedCount

Test data: 20, 45, 60.

session	totalMinutes	condition result	balancedCount
start	-	-	0
1	20	false	0
2	45	true	1
3	60	true	2

Final output: 2

Practice Task 1

points <- 0
FOR question <- 1 TO 4
  INPUT correct
  IF correct = TRUE THEN
    points <- points + 2
  ELSE
    points <- points + 0
  ENDIF
ENDFOR
OUTPUT points

Test data: true, false, true, true.

question	correct	points
start	-
1
2
3
4

Practice Task 2

attempts <- 0
INPUT rating
WHILE rating < 1 OR rating > 5
  attempts <- attempts + 1
  OUTPUT "Enter a value from 1 to 5"
  INPUT rating
ENDWHILE
OUTPUT attempts

Test data: 8, 0, 4.

step	rating	condition result	attempts	output
start	-	-	0
first input	8	true	0
after loop 1	0	true	1	Enter a value from 1 to 5
after loop 2	4	false	2	Enter a value from 1 to 5
final output	4	false	2	2

Practice Task 3

The program should count the number of scores that are 50 or above.

passCount <- 0
FOR item <- 1 TO 5
  INPUT score
  IF score > 50 THEN
    passCount <- passCount + 1
  ENDIF
ENDFOR
OUTPUT passCount

Test data: 50, 51, 49, 70, 30.

Questions

Complete a trace table.
Identify the logical error.
Correct the condition.

Model Answer

The condition should include 50 because the requirement says 50 or above. The corrected condition is:

IF score >= 50 THEN

Trace table practice