Input Validation (OCR GCSE Computer Science)

Revision Note

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Written by: James Woodhouse

Reviewed by: Lucy Kirkham

Input Validation

What is Input Validation?

Input validation is code which is used to check that an input from a user is acceptable and that it matches the requirements of the program
There are 5 main categories of validation which can be carried out on fields and data types, these are
- Length check
- Type check
- Range check
- Presence check
- Format check
There can be occasions where more than one type of validation will be used on a field
An example of this could be a password field which could have a length, presence and type check on it

Length check

Checks the length of a string
An example is ensuring that a password is 8 or more characters in length
Code example

password_length = len(password)

while password_length < 8:
password = input("Enter a password which is 8 or more characters")

Type check

Check the data type of a field
An example is checking a user's age has been entered as an integer, without creating an integer input
Code example

age = input("Enter your age")

while age.isdigit() == False:
print("enter a number")
age = input("Enter your age as a number")

Range check

Ensures the data entered as a number falls within a particular range
An example is checking a user's age has been entered and falls between the digits of 0-100
Code example

age = int(input("Enter your age"))

while age < 0 or age > 100:
age = int(input("Enter your age, ensure it is between 0-100"))

Presence check

Looks to see if any data has been entered in a field
An example is checking that a user has entered a name when registering for a website
Code example

name = input("Enter your name")

while name == "":
name = input("You must enter your name here")

Format check

Ensures that the data has been entered in the correct format
An example would be ensuring that an email includes the @ symbol and a full stop (.)
Code example

email = input("Enter your email address")

while "@" not in email or "." not in email:
email = input("Please enter a valid email address")

Worked Example

A car dealership uses a computer system to record details of the cars that it has for sale. Each car has a make, model, age and number of miles driven.

The car dealership only sells cars that have fewer than 15,000 miles and are 10 years old or less.

Write an algorithm that will:

Ask the user to enter the number of miles and the age of a car
Validate the input to check that only sensible values that are in the given range are entered
Output True if valid data has been entered or False if invalid data has been entered [4]

How to answer this question

When answering any algorithm question, ask yourself:
- What inputs and outputs do I need?
- Do I need to do any calculations or comparisons?
- Do I need to use selection or iteration?
- Do I need to use a function or procedure?
Re-read the algorithm question working through the criteria given

Programming Skill	Algorithm
Inputs	Miles Age
Outputs	True or False
Calculations / Comparisons	Check for valid mileage Check for valid age
Selection or Iteration	Selection is needed (If age <10 and miles < 15000) Iteration is not needed
Function or Procedure	Not needed

Answer:

i)1 mark per bullet, max 4

Miles and age input separately
Checks for valid mileage
Checks for valid age
Checks both are greater than / greater than equal to zero
…correctly outputs both True and False

Example Answer:

miles = int(input("enter miles driven"))
age = int(input("enter age of car"))
valid = True
if miles > 15000 or miles < 0 then
valid = False
elif age > 10 or age < 0 then
valid = False
endif
print(valid)

Last updated: 17 June 2024

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