Computer programs should be designed to ​ (a)   with unexpected or erroneous input from users.

Coders should ​ (b)   for all contingencies that might occur (accidental and ​ (c)   inputs)

• cope
• plan
• deliberate
• handle
• consider

Defensive design is contigency planning using validation, sanitisation, authetication, maintenance and tesing.

What is validation?

• checking an input is sensible and possible

• cleaning up input data

• checking the user is who they say they are

• using sensible variable names, comments and indentation

• Running the program with various test data to remove bugs

Defensive design is contigency planning using validation, sanitisation, authetication, maintenance and tesing.

What is input sanitisation?

• checking an input is sensible and possible

• cleaning up input data

• checking the user is who they say they are

• using sensible variable names, comments and indentation

• Running the program with various test data to remove bugs

Defensive design is contigency planning using validation, sanitisation, authetication, maintenance and tesing.

What is input authentication?

• checking an input is sensible and possible

• cleaning up input data

• checking the user is who they say they are

• using sensible variable names, comments and indentation

• Running the program with various test data to remove bugs

Defensive design is contigency planning using validation, sanitisation, authetication, maintenance and tesing.

What does writing well maintained code involve?

• checking an input is sensible and possible

• cleaning up input data

• checking the user is who they say they are

• using sensible variable names, comments and indentation

• Running the program with various test data to remove bugs

Defensive design is contigency planning using validation, sanitisation, authetication, maintenance and tesing.

What is testing?

• checking an input is sensible and possible

• cleaning up input data

• checking the user is who they say they are

• using sensible variable names, comments and indentation

• Running the program with various test data to remove bugs

Which is the descriptor for presence check?

• Numbers between two given values are accepted

• Data is of a particular specified type

• Data contains an exact number of characters

• Ensures that some data has been entered

Which is the descriptor for range check?

• Numbers between two given values are accepted

• Data is of a particular specified type

• Data contains an exact number of characters

• Ensures that some data has been entered

Which is the descriptor for type check?

• Numbers between two given values are accepted

• Data is of a particular specified type

• Data contains an exact number of characters

• Ensures that some data has been entered

Which is the descriptor for length check?

• Numbers between two given values are accepted

• Data is of a particular specified type

• Data contains an exact number of characters

• Ensures that some data has been entered