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Common exam pitfall
Students often confuse range check (which checks numerical values) with length check (which counts the number of characters in a string).
Validation is an automatic computer check performed by software to ensure that data entered into a system is sensible, reasonable, and conforms to predefined rules before it is processed or committed to a database.
1. The Critical Distinction
Note: Exam Golden Rule: Validation DOES NOT check if data is factually correct. It only checks whether the data is acceptable according to the rules of the system. For example: If a student types their name as "Dvaid" instead of "David", a validation check will accept it because "Dvaid" satisfies presence, length, and character-type checks!
2. The Six Standard Validation Checks
Validation Check | Definition / Rule Tested | Concrete Example |
|---|---|---|
Range Check | Verifies that a numerical or date value falls between an upper and lower boundary. | Month must satisfy $1 \le \text{Month} \le 12$. Exam score $0 \le \text{Mark} \le 100$. |
Length Check | Verifies that a string contains either an exact number of characters or falls within minimum/maximum limits. | Password must be $\ge 8$ characters. PIN text must contain exactly 4 characters; a separate format check can require digits. |
Type Check | Verifies that the value has the expected data type. | Age must be an integer. A STRING type alone does not restrict a surname to letters; a separate format rule is needed. |
Presence Check | Verifies that a mandatory data field has not been left blank or empty. | National Insurance number or Email address field cannot be empty. |
Format Check | Verifies that text conforms to a specific pattern or character mask. | Postal code matching |
Check Digit | A calculated value appended to the end of a numerical code to detect transmission, transcription, or transposition errors. | Final digit of an ISBN-13 book code or EAN-13 barcode recalculated via modulo arithmetic. |
3. Implementing Validation in Cambridge Pseudocode
Input validation loops ensure incorrect entries are rejected immediately and re-prompted:
DECLARE StudentAge : INTEGER
REPEAT
OUTPUT "Enter student age (11 to 18): "
INPUT StudentAge
IF (StudentAge < 11) OR (StudentAge > 18) THEN
OUTPUT "Invalid age! Must be between 11 and 18."
ENDIF
UNTIL (StudentAge >= 11) AND (StudentAge <= 18)
OUTPUT "Valid age recorded: ", StudentAgeNotice that the REPEAT ... UNTIL loop checks the valid condition at the bottom to exit.
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Exam-Style Check: Match Validation Checks to Data Input Scenarios
Match each validation check with its application scenario:
Interactive exercises for Module 2 and beyond require an active plan.