3.2.5 - Writing Maintainable Programs

3.2.5 - Writing Maintainable Programs

1. Key Terms

   • Variable
     • Name associated with a particular memory location used to store data.
     • By using the variable name, the programmer can:
       • Store data
       • Retrieve data
       • Manipulate data
     • The value of the data is not know when the program is written.
     • Scope
       • Local variable
         • Declared and used inside:
           • Modules
           • Functions
           • Procedures
           • Subroutines
         • Only available inside their specified module, procedure etc...
         • Created when the subroutine is called.
         • Destroyed when the subroutine exits.
       • Global variable
         • Declared at the beginning of the code.
         • Available throughout the code.
     • Can change while the program is running.
   • Constant
     • A data item with a fixed value.
     • Assigned to a variable that cannot be changed when the program is executed.
   • Identifier
     • A name representing an object within a program.
       • Variables
       • Functions
       • Procedures
       • Data Types
     • Given meaningful names.
   • Reserved Word / Keyword
     • Vocabulary of a programming language.
     • Variables or other identifiers cannot use keywords.
     • Can only have the meaning which is defined in the language.

2. Coding Practices

   • Modularisation
     • Series of small routines.
     • Can quickly be seen to be performing one function.
     • Complex operations should be broken up into subroutines.
       • Defined separately and called from the main program.
     • Easier way to achieve if the program has been designed using top-down techniques.
   • Commenting Code
     • Comments are read by the programmer and ignored by the computer.
     • Should be written while the code is written and not after.
     • Comments should be used for:
       • Program headers
       • Subroutines
       • Declaring variables
       • Inline comments
   • Indentation
     • Improves readability.