Pseudocode for validating input

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. Which pseudocode correctly keeps asking until the age is in the range 12 to 18?

A input age while age < 12 OR age > 18 print "Age must be 12-18" input age end while

B input age while age < 12 AND age > 18 print "Age must be 12-18" input age end while

2. A validation loop repeats while the input is...

A valid

B invalid

3. Which condition is a presence check for a variable called name?

A while name = ""

B while name > 100

4. Which loop body is the best way to handle invalid input?

A input score print "Invalid, try again"

B print "Invalid, try again" input score

5. Why must the loop body include a second input statement?

A So the user can enter a new value and the condition can be tested again

B So the program can store the input twice

Match the Pairs

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

Left column		Right column
1WHILE age < 12 OR age > 18		AA range check condition: the loop keeps repeating while the age falls outside the allowed range of 12 to 18
2WHILE name = ""		BThe loop never asks for input again, so age never changes and the loop repeats forever after an invalid entry.
3After a failed check, show an error message and ask the user to enter the value again inside the loop		CA presence check condition: the loop repeats while nothing has been entered
4Read the first input before the loop so the condition has a value to test		Dinput age WHILE age < 12 OR age > 18 print "Age must be 12 to 18" input age ENDWHILE
5input age WHILE age < 12 OR age > 18 print "Age must be 12 to 18" ENDWHILE		EThe condition tests for VALID input, so the loop runs and shows an error when the age is correct, but accepts invalid ages.
6input age WHILE age >= 12 AND age <= 18 print "Age must be 12 to 18" input age ENDWHILE		FWHILE score < 0 OR score > 100 print "Enter a score from 0 to 100" input score ENDWHILE

Definitions

while input is invalid

Fill in the Blanks

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

while age < 1 __ age > 120 print "Age must be 1-120" input age

while LENGTH(name) = _ print "Name cannot be blank" input name

while mark < 0 OR mark > 100 _____ "Mark must be 0-100" input mark

while score < 0 OR score > 10 print "Enter a score from 0 to 10" _____ score

while LENGTH(pin) _ 4 print "PIN must be 4 digits" input pin

Spot the Error

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

Question 1

A input age

B while age < 1 and age > 120

C print "Invalid age"

D input age

E end while

Question 2

A print "Enter name"

B input name

C while name <> ""

D print "Name required"

E input name

F end while

Question 3

A print score

B while score < 0 or score > 100

C print "Enter 0 to 100"

D input score

E end while

Question 4

A input level

B while level < 1 or level > 10

C print "Enter 1 to 10"

D print level

E end while

Question 5

A input password

B while length(password) > 8

C print "Min 8 characters"

D input password

E end while

Answer Key

Pseudocode for validating input

Section A: Quick Questions

A — input age while age < 12 OR age > 18 print "Age must be 12-18" input age end while

B — invalid

A — while name = ""

B — print "Invalid, try again" input score

A — So the user can enter a new value and the condition can be tested again

Section B: Match the Pairs

WHILE age < 12 OR age > 18 → A range check condition: the loop keeps repeating while the age falls outside the allowed range of 12 to 18

WHILE name = "" → A presence check condition: the loop repeats while nothing has been entered

After a failed check, show an error message and ask the user to enter the value again inside the loop → WHILE score < 0 OR score > 100 print "Enter a score from 0 to 100" input score ENDWHILE

Read the first input before the loop so the condition has a value to test → input age WHILE age < 12 OR age > 18 print "Age must be 12 to 18" input age ENDWHILE

input age WHILE age < 12 OR age > 18 print "Age must be 12 to 18" ENDWHILE → The loop never asks for input again, so age never changes and the loop repeats forever after an invalid entry.

input age WHILE age >= 12 AND age <= 18 print "Age must be 12 to 18" input age ENDWHILE → The condition tests for VALID input, so the loop runs and shows an error when the age is correct, but accepts invalid ages.

Section C: Definitions

while input is invalid — A loop that reads input, tests it (presence, type, range or length), then shows an error message and asks again until the input passes the check.

Section D: Fill in the Blanks

while age < 1 OR age > 120
  print "Age must be 1-120"
  input age

while LENGTH(name) = 0
  print "Name cannot be blank"
  input name

while mark < 0 OR mark > 100
  print "Mark must be 0-100"
  input mark

while score < 0 OR score > 10
  print "Enter a score from 0 to 10"
  input score

while LENGTH(pin) ≠ 4
  print "PIN must be 4 digits"
  input pin

Section E: Spot the Error

B — No age can be below 1 and above 120 at once, so the loop never runs and bad input gets through. Use 'or' so the loop repeats when the age is outside the range.

C — A presence check should loop while the name is empty (name = ""). With <> the loop runs when a name has been entered, and it stops when the input is blank. It should be: while name = ""

A — The program must read a value with 'input score' before the loop tests it. 'print score' only displays a variable that has no value yet.

D — After the error message the program must ask again with 'input level'. Printing the old value never changes it, so the loop repeats forever.

B — The length check should repeat while the password is too short (length < 8). Using > rejects long passwords and accepts short ones.