2.3.1

• Defensive design considerations:

  • Anticipate how users might misuse a program, then attempt to prevent it from happening
  • Authentication
  • Ensure code is well maintained
  • Reduce errors
• Input validation


  Checking is data meets certain criteria before passing it into the program, e.g. checking that an email address contains an @ symbol and has a suitable ending
• Types of input validation check

  • Range check- Checks the data is within a specified range
  • Presence check- Checks that data has been entered
  • Format check- Checks the data has the correct format, e.g. a date
  • Look-up table- Checks the data against a table of acceptable values
  • Length check- Checks the data is the correct length
  • Type check- Checks data is of the right data type
• Maintainability:


  Using sub programs can make it easier for other programmers to see how different parts of a program work, which can help them understand the overall program faster
• Maintainability

  • Enabling future maintenance of your program
  • Making it easier for future support programmers to identify and fix problems
  • Making it easier to extend your original program if customer has additional requirements
• Maintainability:

  Use comments to:

  • Explain the purpose of the program
  • Explain sections of code
  • Explain unusual approach's
  • Visually divide sections of a program
• Maintainability:

  Use indentation for every selection and iteration branch
• Maintainability:

  Use descriptive variable names using naming conventions

  • Explain their purpose
  • Constant declared at the top of a program
• Maintainability:

  Use sub routines to:

  • Structure the code
  • Eliminate duplicating code
  • Make it easier/faster to reuse code