F452 - 3.2.5 Writing Maintainable Programs


3.2.5 Writing Maintainable Programs

These are short definitions of key terms for writing maintainable programs.


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  • Most languages insist that identifiers begin with a letter.
  • When declaring variables, programmer should use meaningful identifiers.
  • For this reason single letter identifiers should be avoided.
  • As spaces are not allowed, use underscores/capitalisation appropriately.
  • Use prefixes at the start of indetifier names to remind you of the data type.
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When declaring variables/constants, programmer must be aware of scope.

  • Local variables are declared and used inside a module/subroutine.
  • Global variables are declared at beginning of the code; available throughout.

Using local variables as far as possible - good programming style.

Some programming languages will initialise variables (when they are declared).

  • This basically means that the variables are given a starting value.

Generally integers are set to 0, Booleans are set to FALSE and strings are empty.

Constants can make code easier to read and maintain.

  • Many programs contain values that don't change whilst the program is running
  • These may be universal constants that are always the same.
  • New programmers tend to use literals in their code for such values.
    • This means that the code contains the actual values spelt out in full.
  • As a general rule literals SHOULD BE AVOIDED in code.
  • They should be SUBSTITUTED WITH CONSTANTS unless there is a good reason not to.
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Modularised code makes the program easier to understand.

  • Code should be written as a series of small routines.
  • Complex operations should be broken into subroutines (defined separately).
  • Modularisation is easier to achieve if top-down techniques have been utilised.


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  • Most languages allow comments to be inserte.
  • These are read by the programmer, and ignored by the computer.
  • Comments are vital  to making the code understandable.
  • They should be written as the code is, not after.
    • Subroutines should have comments explaining what it does.
    • Variables and constants should have their purpose explained.
    • Code itself should use inline comments explaining stages of the algorithm.
  • Comments shouldn't however simply repeat the code.
  • They must not clutter the program and potentially add confusion.
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