← ACARA Digital Technologies Years 9–10

Format checking text and dates

A validation check that tests a value follows an expected pattern, like two letters then three digits or a real date. A correct pattern does not prove the data is right.

Part of: ACARA Digital Technologies Years 9–10 — Acquiring and Validating Data — Module 75

Understanding Format checking text and dates in ACARA Digital Technologies Years 9–10

What it does: RIGHT takes the last three characters and multiplying by 1 turns them into a number only if they are digits, so ISNUMBER tests the digit part of the pattern. Real dates are stored as numbers, so ISNUMBER is TRUE for them. 31 February does not exist, so the entry stays text and ISNUMBER is FALSE. There is no day 45 and no month 13, so 45/13/2025 is not a real date. 14/03/2025 is a real date. A12B3 mixes letters and digits in the wrong places. KT482 has two letters followed by three digits, so it passes. A format check only confirms the pattern. KT482 might belong to a different student or might not exist at all, so other checks and verification are still needed.

Common mistakes: A code like AB123 has its three digits at the END. LEFT takes characters from the start, so it would grab letters. It should be RIGHT(code, 3). A code of two letters then three digits is 5 characters long, not 3. The length test should be LEN(code) = 5.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 255–329) and word search (Modules 226–329).

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Learning
Duo
What does a format check do?
Tests that a value follows an expected patternTests that a value is true in real life
Matches
=ISNUMBER(LEFT(A2,2)) to check a code starts with two digits
↓
LEFT returns text, even when it looks like digits, so ISNUMBER gives FALSE. Multiply by 1 first, as in ISNUMBER(LEFT(A2,2)*1).
Applying
Meanings
Term
format check
Meaning
A validation check that tests a value follows an expected pattern, like two letters then three digits or a real date. A correct pattern does not prove the data is right.
Practice
=IF(ISNUMBER(VALUE(RIGHT(B2,2))),"Format OK","Bad format")
Testing
Gaps
=ISNUMBER(VALUE((A2,3)))
Check Answer
Spots
2letters ← LEFT(code, 2)
3digits ← LEFT(code, 3)

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Quick Questions

1. What does a format check do?
A. Tests that a value is true in real life
B. Tests that a value follows an expected pattern ✓
A format check only looks at the pattern, such as two letters then three digits. It cannot tell whether the value is actually true.
2. Student IDs look like KT482 (two letters then three digits). Which formula pulls out the letters part to test?
A. =RIGHT(A2,2)
B. =LEFT(A2,2) ✓
LEFT takes characters from the start of the text. The two letters come first, so LEFT(A2,2) gets them.
3. Student IDs look like KT482. Which formula pulls out the three digits at the end?
A. =RIGHT(A2,3) ✓
B. =LEFT(A2,3)
RIGHT takes characters from the end of the text, so RIGHT(A2,3) returns the last three characters.
4. Which formula correctly tests that the last three characters of A2 are digits?
A. =ISNUMBER(VALUE(RIGHT(A2,3))) ✓
B. =ISNUMBER(RIGHT(A2,3))
RIGHT returns text, even when it looks like digits. ISNUMBER on that text gives FALSE, so VALUE is needed to convert it to a number first.
5. A2 holds 31/02/2025, which the spreadsheet could not read as a real date, so it stays as text. What does =ISNUMBER(A2) return?
A. FALSE ✓
B. TRUE
Real dates are stored as numbers, so ISNUMBER is TRUE for them. 31 February does not exist, so the entry stays text and ISNUMBER is FALSE.

Match the Pairs

=ISNUMBER(LEFT(A2,2)*1) → Tests whether the first two characters of a code are numbers, which would be wrong for a code that should start with letters
=ISNUMBER(B2) → Checks that a date was entered as a real date, because spreadsheets store real dates as numbers
A format check on a code of two letters then three digits can test the last three characters with RIGHT → =ISNUMBER(RIGHT(A2,3)*1)
A value can pass a format check and still be wrong, so the check does not prove the data is correct → AB123 passes the pattern but is not a real student ID
=ISNUMBER(LEFT(A2,2)) to check a code starts with two digits → LEFT returns text, even when it looks like digits, so ISNUMBER gives FALSE. Multiply by 1 first, as in ISNUMBER(LEFT(A2,2)*1).
Date entered as 31/02/2025 is accepted because it looks like dd/mm/yyyy → The pattern looks right but 31 February is not a real date. A format check needs to test for a real date, not just the look of one.

Key Term

format check
A validation check that tests a value follows an expected pattern, like two letters then three digits or a real date. A correct pattern does not prove the data is right.

Fill in the Blanks

1. =ISNUMBER(VALUE(RIGHT(A2,3)))
Hint: Type the function that takes characters from the end of the text, to test the three digits.
2. =IF(LEFT(A2,2)="AB","Prefix OK","Bad")
Hint: Type the function that takes characters from the start of the text, to test the two letters.
3. =IF(ISNUMBER(B2),"Real date","Not a date")
Hint: Type the function that tests whether a cell holds a number, because real dates are stored as numbers.
4. =RIGHT(A2,3)
Hint: Type how many characters make up the digits part of a code with two letters then three digits.
5. =AND(ISNUMBER(B2),B2<=TODAY())
Hint: Type the comparison operator meaning on or before, so a correct date pattern is also checked as not in the future.

Spot the Error

Question 1
A code ← A2
B letters ← LEFT(code, 2)
C digits ← LEFT(code, 3)
D ok ← ISNUMBER(VALUE(digits))
Line C — A code like AB123 has its three digits at the END. LEFT takes characters from the start, so it would grab letters. It should be RIGHT(code, 3).
Question 2
A code ← A2
B ok ← LEN(code) = 3
C IF ok THEN accept code
Line B — A code of two letters then three digits is 5 characters long, not 3. The length test should be LEN(code) = 5.
Question 3
A date ← A2
B isDate ← ISNUMBER(date)
C IF isDate = TRUE THEN
D SHOW 'Not a real date'
E ELSE
F SHOW 'Not a real date'
Line D — This is the branch for when ISNUMBER returns TRUE, so the message should say 'Real date'. As written, both branches give the same message and the check tells the user nothing.
Question 4
A letters ← RIGHT(code, 2)
B digits ← RIGHT(code, 3)
C ok ← ISNUMBER(VALUE(digits))
Line A — The two letters come at the start of the code, so you need LEFT(code, 2). RIGHT would take the last two digits instead.
Question 5
A d ← '31/02/2026'
B ok ← ISNUMBER(DATEVALUE(d))
C IF ok = TRUE THEN reject d
Line C — 31/02/2026 is not a real date, so ok is FALSE and the entry should be rejected. The broken line rejects dates that pass the check. It should test ok = FALSE.

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