2.3 Producing robust programs

2.3 Producing robust programs

1. data validation

   • check to ensure that the data entered is sensible and reasonable. It does not check the accuracy of data.

2. data sanitisation

   • trims or strips strings removing unwanted characters to make sure it contains only permitted characters e.g. D%ave the % would be removed

3. authenticication

   • the process of verifying the identify of a user or process

4. maintainability

   • updating code so that it is compatible with current requirements

5. comments

   • to help describe the code and structures in a program using #

6. indentation

   • used to show the programs structure e.g. where selection or iteration or functions are used

7. Data validation and verification methods

   • check digit
     • The last one or two digits in a code are used to check the other digits are correct
       • e.g. Bar code readers in supermarkets use check digits
   • format check
     • Checks the data is in the right format
       • e.g. A National Insurance number is in the form LL 99 99 99 L where L is any letter and 9 is any number
   • length check
     • Checks the data isn't too short or too long
       • e.g. A password which needs to be six letters long
   • lookup table
     • Looks up acceptable values in a table
       • e.g. There are only seven possible days of the week
   • presence check
     • Checks that data has been entered into a field
       • e.g. In most databases a key field cannot be left blank
   • range check
     • Checks that a value falls within the specified range
       • e.g. Number of hours worked must be less than 50 and more than 0
   • spell check
     • Looks up words in a dictionary
       • e.g. When word processing

8. anticipating missuse

   • Defensive program design will consider and anticipate misuse. Misuse may be in the form of a brute force attack on the program. E.G Many programs and systems only allow a user to enter a password three or four times before it locks out the system.

9. contingency palnning

   • Once a programmer has anticipated the misuse they can then plan for the these issues. For example: Limiting the number of logon attempts. Ensuring the code is robust in validating the data entered

10. testing and errors

    • iterative testing
      • This happens overtime and is repeated throughout the development of the program
    • final/terminal teting
      • when the product is released and real end users begin using it. Very often, end users find things wrong with systems that the programmers did not expect.
    • syntax errors
      • error in the rules/grammar of the language Eg missing colon / spelling mistake
    • logic errors
      • The program is written to do something other than what the programmer intended Eg Resetting only the first 9 elements in an array instead of all 10.
    • test data
      • Something which has been specifically identified for use in tests, typically of a computer program