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Cambridge IGCSE Computer Science · 0478

Topic 7: Algorithm Design and Problem-Solving — Part 2

Validation, Verification & Test Data

Validation and verification

Validation is an automated check that data is reasonable and fits the rules before it is accepted. Common validation checks include:

Check type What it checks Example
Range check Value is within allowed limits Month integer must be between 1 and 12
Length check Correct number of characters Password must contain at least 8 characters
Type check Data is the correct data type An employee count field must accept integers only
Presence check A required field is not left empty Contact email address field cannot be left empty
Format check Data matches a required pattern Date must match the layout DD/MM/YYYY
Check digit An extra digit confirms the rest of the data is correct ISBN or barcode last digit verifies the code

Verification checks that data matches the original source — it confirms accuracy, not just reasonableness. Two common methods are:

  • Visual check — a person reads data from a source document and compares it with what was entered (e.g. checking a typed form against a paper application).
  • Double entry check — critical data is entered twice into separate fields (e.g. a new PIN or email during registration); the system alerts the user if the two entries do not match.

Implementing checks in pseudocode:

A visual check is performed by a person and is not usually written as program code. A double-entry verification can be implemented as follows:

INPUT Password
INPUT ConfirmPassword
IF Password <> ConfirmPassword THEN
    OUTPUT "Passwords do not match — please re-enter"
ELSE
    OUTPUT "Password accepted"
ENDIF

A range validation (automated check that data is reasonable) looks like this:

INPUT Age
IF Age < 0 OR Age > 120 THEN
    OUTPUT "Invalid age"
ELSE
    OUTPUT "Age accepted"
ENDIF

Test data types

When testing a program that accepts values in the range 1 to 100, use four types of test data:

Test data type Description Example (range 1–100)
Normal Typical valid data within the range 25, 50, or 88
Abnormal Clearly invalid data that should be rejected -12, 145, or "Excellent"
Extreme The largest or smallest valid values in the range 1 and 100
Boundary Values on the edge of the valid range — the valid extreme and the next invalid value 0, 1, 100, and 101
Number line showing valid range 1 to 100 with normal, abnormal, extreme, and boundary test data values marked
Diagram 1: Test data for a range check of 1–100 — normal values sit inside the range, extremes are the valid limits, and boundary values include the valid extreme plus the next invalid value.

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