Validation | Computer for GCSE/IGCSE - Year 11 PDF Download

Introduction

• Validation and verification ensure input data correctness, reasonableness, and accuracy.
• Validation ensures data adherence to specified rules by programmers, while verification double-checks data for user intent.

Validation

• Validation involves verifying input data to ensure it meets expected criteria, making it suitable for system acceptance.
• Programmers establish rules within the code to automatically validate user input data, rejecting unreasonable entries. If rejected, users are typically provided with a message explaining the issue and given the opportunity to re-enter the data.
• The different types of validation rules or checks are as follows:
  • Range Checks
  • Length Checks
  • Type Checks
  • Presence Checks
  • Format Checks
  • Check Digits
• Each piece of data may require multiple different checks to be fully valid.

Range Checks

• Range checks ensure that input data falls within a specified range defined by the user, such as a percentage between 0 and 100 or a date falling within the inclusive range of 1 to 30 for April.

OUTPUT “Enter a number between 0 and 100”
REPEAT
INPUT Number
IF Number < 0 OR Number > 100
  THEN
OUTPUT “Number is not between 0 and 100, please try again”
ENDIF
UNTIL Number >= 0 AND Number <= 100

Length Check

• Definition: Length checks verify if input data meets specified character criteria.
• Example: A 4-digit bank PIN must be exactly 4 characters long; otherwise, it is rejected.
• User Prompt: Request the user to input their 4-digit bank PIN number.
• Validation: If the length of the PIN is not 4, prompt the user to try again with a 4-character PIN.

OUTPUT “Please enter your 4 digit bank PIN number”
REPEAT
INPUT Pin
IF LENGTH(Pin) <> 4
THEN
OUTPUT “Your pin number must be four characters in length, please try again”
ENDIF
UNTIL LENGTH(Pin) = 4

• Passwords typically have a designated length requirement, such as being between eight and twenty characters. Any password falling outside this range should be declined.

OUTPUT “Please enter a password between 8 and 20 characters”
REPEAT
INPUT Password
IF LENGTH(Password) < 8 OR LENGTH(Password) > 20
THEN
OUTPUT “Your password must be between 8 and 20 characters in length, please try again”
ENDIF
UNTIL LENGTH(Password) >= 8 AND LENGTH(Password) <= 20

Type Checks

• Type checks verify that input data is of the correct data type. For instance, ensuring that someone's age is an integer and their name is a string.

OUTPUT “Enter an integer number”
REPEAT
INPUT Number
IF Number <> DIV(Number, 1)
  THEN
OUTPUT “Not a whole number, please try again”
ENDIF
UNTIL Number = DIV(Number , 1)

Presence Checks

• Presence checks confirm that input data has been provided and that input fields are not left empty.
• Systems like login authentication require presence checks for essential fields like usernames and passwords.

OUTPUT “Enter your username”
REPEAT
INPUT Username
IF Username = “”
THEN
OUTPUT “No username entered, please try again”
ENDIF
UNTIL Username <> “”

Format check

• Format checks ensure that input data follows a specific pattern.
• Identification codes like 'AP1234' and dates represent examples of patterns.
• Format checks involve pattern matching and string handling processes.
• The algorithm verifies a six-digit identification number against the format "XX9999".
• Here, 'X' stands for an uppercase alphabetical letter and '9999' signifies a four-digit number.
• Initial two characters are matched with a list of approved characters.
• If a match is found, the loop stops, and the character is marked as valid.
• Digit characters are cast into numbers for validation.
• Validation includes checking if the digits fall within the range of 0-9999.
• If any checks fail, the algorithm outputs an appropriate error message.

INPUT IDNumber
IF LENGTH(IDNumber) <> 6
  THEN
OUTPUT “ID number must be 6 characters long”
END IF
ValidChars ← “ABCDEFGHIJKLMNOPQRSTUVWXYZ”
FirstChar ← SUBSTRING(IDNumber, 1, 1)
ValidChar ← False
Index ← 1
WHILE Index <= LENGTH(ValidChars) AND ValidChar = False DO
IF FirstChar = ValidChars[Index]
  THEN
ValidChar ← True
ENDIF
Index ← Index + 1
ENDWHILE
IF ValidChar = False
  THEN
OUTPUT “First character is not a valid uppercase alphabetical character”
ENDIF
SecondChar ← SUBSTRING(IDNumber, 2, 2)
ValidChar ← False
Index ← 1
WHILE Index <= LENGTH(ValidChars) AND ValidChar = False DO
IF SecondChar = ValidChars[Index]
  THEN
ValidChar ← True
ENDIF
Index ← Index + 1
ENDWHILE
IF ValidChar = False
 THEN
OUTPUT “Second character is not a valid uppercase alphabetical character”
ENDIF
Digits ← INT(SUBSTRING(IDNumber, 3, 6))
IF Digits < 0000 OR Digits > 9999
  THEN
OUTPUT “Digits invalid. Enter four valid digits in the range 0000-9999”
ENDIF

Check digits

• Check digits are single digits found at the end of codes like barcodes or ISBNs. They are calculated using a specific algorithm and are added to the code for error detection.
• These digits play a crucial role in spotting errors that may occur during data entry, such as typing mistakes, scanning errors, or verbal slip-ups.
  • Common errors that check digits help identify include missing or extra digits, digits that are swapped, mispronounced numbers, or simply incorrect digits.

Barcode ← “9780201379624”
Total ← 0
FOR Index = 1 to LENGTH(Barcode) - 1
IF Index MOD 2 = 0
THEN
Total ← Total + CAST_TO_INT(Barcode[Index])*3
ELSE
Total ← Total + CAST_TO_INT(Barcode[Index])*1
ENDIF
NEXT Index
CheckDigit ← 10 - Total MOD 10
IF CheckDigit = Barcode[LENGTH(Barcode)]
  THEN
OUTPUT “Valid check digit”
ELSE
OUTPUT “Invalid check digit”
ENDIF

Verification

• Verification involves ensuring that the data entered into a system is accurate. 
• Mistakes like creating a new account or inputting a password incorrectly can lead to immediate lockout from the account.
• Methods of verification include double entry checking and visual checks.

Double Entry Checking

• Double entry checking requires entering data twice into separate input boxes and then comparing the entries to confirm they match. If there is a discrepancy, an error message will be displayed.

REPEAT
OUTPUT “Enter your password”
INPUT Password
OUTPUT “Please confirm your password”
INPUT ConfirmPassword
IF Password <> ConfirmPassword
THEN
OUTPUT “Passwords do not match, please try again”
ENDIF
UNTIL Password = ConfirmPassword

Visual Check

• Visual checks entail users visually inspecting the displayed data on the screen. Following this, a popup or message prompts the user to confirm the accuracy of the data before proceeding. If incorrect, users re-enter the data.

REPEAT
OUTPUT “Enter your name”
INPUT Name
OUTPUT “Your name is: “, Name, “. Is this correct? (y/n)”
INPUT Answer
UNTIL Answer = “y”