Pseudocode: validating a record before insertion

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Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. A record has three fields to check before insertion. When should the record be inserted?

A Only if every check passes and the valid flag is still true

B As soon as the first check passes

2. Which line sets up a valid flag before the checks begin?

A valid <- true

B valid = true <- if

3. A check finds that the age field is -5. What should the pseudocode do with the flag?

A valid <- true

B valid <- false

4. Which is the correct way to guard the insertion?

A if valid = true then INSERT record

B if valid <- true then INSERT record

5. What is a sensible action for a record that fails validation?

A Insert it anyway and fix it later

B Skip it, or report an error message about it, and move on to the next record

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1valid <- true		AThe else branch resets valid to true, which wipes out a failure from an earlier check. Set valid to true once at the start and only ever change it to false.
2if valid = true then INSERT record		BInsert the record only if every validation check left the valid flag true.
3A failed check sets the flag to false so the record will not be inserted		CThe record is inserted before the check runs, so a bad record is inserted anyway. The INSERT must come after the checks and sit inside if valid = true then.
4A record with a missing (null) field is rejected as invalid and reported instead of inserted		Dif name = null then valid <- false
5valid <- true INSERT record if age < 0 then valid <- false		EStart by assuming the record is valid. Each failing check will later change this flag to false.
6if age < 0 then valid <- false else valid <- true		Fif age < 0 then valid <- false

Definitions

if valid = true then

Fill in the Blanks

Complete each line of code by filling in the missing parts.

valid ← ____ if age < 0 then valid ← false

if age < 0 __ age > 120 then valid ← false

if valid = true then ______ record into students

if name = ____ then valid ← false

if valid = true then insert record into students else _____ "Record skipped"

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A valid <- true

B if age > 0 then

C valid <- false

D end if

E if valid = true then

F insert record

Question 2

A valid <- true

B if height <= 0 then

C print 'Bad height'

D valid <- true

E end if

F if valid then insert record

Question 3

A if valid = false then

B insert record

C else

D print 'Record skipped'

E end if

Question 4

A valid <- true

B if mark < 0 then

C valid = false

D end if

E if valid = true then

F insert record

Question 5

A valid <- false

B if dob = null then

C valid <- false

D print 'DOB is missing'

E end if

F if valid then insert record

Answer Key

Pseudocode: validating a record before insertion

Section A: Quick Questions

A — Only if every check passes and the valid flag is still true

A — valid <- true

B — valid <- false

A — if valid = true then INSERT record

B — Skip it, or report an error message about it, and move on to the next record

Section B: Match the Pairs

valid <- true → Start by assuming the record is valid. Each failing check will later change this flag to false.

if valid = true then INSERT record → Insert the record only if every validation check left the valid flag true.

A failed check sets the flag to false so the record will not be inserted → if age < 0 then valid <- false

A record with a missing (null) field is rejected as invalid and reported instead of inserted → if name = null then valid <- false

valid <- true INSERT record if age < 0 then valid <- false → The record is inserted before the check runs, so a bad record is inserted anyway. The INSERT must come after the checks and sit inside if valid = true then.

if age < 0 then valid <- false else valid <- true → The else branch resets valid to true, which wipes out a failure from an earlier check. Set valid to true once at the start and only ever change it to false.

Section C: Definitions

if valid = true then — Only insert the record if every validation check left the valid flag true. If any check set valid to false, skip the bad record or report it instead of inserting it.

Section D: Fill in the Blanks

valid ← true
if age < 0 then valid ← false

if age < 0 or age > 120 then
  valid ← false

if valid = true then
  insert record into students

if name = null then valid ← false

if valid = true then
  insert record into students
else print "Record skipped"

Section E: Spot the Error

B — The age check is reversed. It flags every positive age as invalid and lets negative ages through. A bad age is one that is less than 0, so it should be: if age < 0 then.

D — After reporting the bad height, the check must set the flag to false so the record is not inserted. Setting it to true leaves a bad record marked as valid. It should be: valid <- false.

A — The record should only be inserted when the valid flag is true. Testing for false inserts the bad records and skips the good ones. It should be: if valid = true then.

C — In pseudocode, assignment uses the arrow <-. Writing = compares values and does not change the flag. It should be: valid <- false.

A — The flag must start as true and only be changed to false when a check fails. If it starts as false, every record is rejected even when all checks pass. It should be: valid <- true.