Presence, length, type and format checks

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Start with the concept and its key vocabulary.

Key idea

Describe common validation types and implement presence, length and simple format checks with loops.

Different inputs need different validation. A presence check rejects a blank string. A length check measures characters. A type check asks whether the data has the required type, while a format check examines its pattern, such as DD/MM/YYYY. A look-up check compares input with known allowed values. More than one rule may be needed, and a loop repeats until all required checks pass.

Presence check

A validation check that ensures data has been entered and is not blank.

Length check

A validation check that ensures input has the required number of characters.

Type check

A validation check that ensures data has the required data type.

Format check

A validation check that ensures data follows a required pattern or structure.

Look-up check

A validation check that compares input with a predefined list of allowed values.

Keep these in mind

Presence means the input is not an empty string.
Length checks use .length in ERL and len() in Python.
A type check concerns the kind of data, not whether its value is true.
Casting with int() is not itself a type check: unsuitable text causes a runtime error unless the program validates or safely handles it.
A format check tests a pattern, such as a separator in a fixed position.
A look-up check compares against a predefined allowed collection.
All required validations must pass before input is accepted.

Describe common validation types and implement presence, length and simple format checks with loops.