Defensive Design

Defensive Design

1. Defensive design helps ensure that programs function properly

   • When programs are functioning correctly they should never break and never produce errors
     • A whitelist is all of the data that a program should accept
     • A blacklist is all of the data that a program should reject
   • Programmers try to protect their programs through defensive design
   • There are two ways you can prevent users from entering something that you don't want them to
     • INPUT SANITATION - removing any unwanted characters before passing data through the program
     • INPUT VALIDATION - Checking that data meets certain criteria before passing it into the program
   • Authentication helps protect your program
     • Authentication can confirm the identity of a user before they are allowed to gain access to certain parts of the program
     • Passwords are usually associated with a username. When someone tries to access a protected part of the program it should ask for who their password to confirm identity

2. Testing

   • Programming errors can be syntax or Logic
     • Syntax Error
       • When a compiler or an interpreter doesn't understand what something you've typed because it doesn't follow the programming language
       • These can be diagnosed by compilers or interpreters - they'll be unable to turn the source code into a machine code and a syntax error will be returned
     • Logic Error
       • When the compiler or interpreter is able to run the program , but the program does something unexpected
       • Logic errors are harder to diagnose and track down- compilers and interpreters will not pick them up

3. Translators

   • Computer languages can either be high level or low level
     • Most programming languages are high-level. Its easy for humans to write but computers need to translate it to machine code before they can run it.
     • Low level languages are harder for humans to read and write but easier for the computer to run.
   • Translators convert programming language into Machine Code
   • There are 3 types of translators : assemblers, compilers and Interpreters
   • A compiler translates all of the source code at the same time and creates one executable file. Runs quicker
   • An interpreter runs the source code one instruction at a time, but doesn't create an executable file. Runs slowly

4. Integrated Development Environments

   • IDE's have lots of features to help programmers
     • An integrated development environment is a piece of soft ware that provides features to help a programmer to develop their program
       • The code editor is the main part of the IDE, its where the code is written.
         • Good code editors will have auto-correct, auto-indentation and auto-complete
       • Run- time environment allows the code to be run quickly within the IDE
       • Error diagnostics and debugging tools help find and fix errors
         • They will tell you the location of the error and suggest a way to fix it
       • A GUI helps the programmer design a user interface by building it up graphically rather than having to design it using the source code