F452 - Maintainable code

Programs should be written so that they are easy for any programmer to understand, debug and modify.

Why write maintainable code?

• Make errors less likely.
• Make errors easier to spot.
• Programmers working in a team can understand each other's code.
• If the code needs to be revisited later, the time needed to familiarise yourself with the program is reduced.

Variable & constants: definitions?

• Variable: 

The name used to refer to a particular memory location used to store data of a particular type which may change as the program is running.

• Constant: 

The name used to store a fixed value. The value is set when the code is written and cannot be changed while the program is running.

• Identifier: 

The name given to a variable, a constant or a subroutine.

Choosing Identifiers?

• Must begin with a letter.
• May contain letter, digits and underscores.
• Should be meaningful... They should describe the purpose of the variable or constant.
• Use underscores_ or CamelCase to divide words.
• Use standard conventions to indicate data types.
• Avoid reserve words (keywords).
• Variables should be initialised before being used in an expression.
• Constants should be declared at the beginning of the program or subroutine.

Scope or Variables & Constants?

Usually LOCAL or GLOBAL.

Refers to the part of the program in which a variable or constant can be used.

Local:

Declared within a subroutine and only available for use within that subroutine.

Pros: Saves space; able to reuse names.

Global:

Declared at the beginning of the program and available throughout the code.

Pros: Eases data passing between parts of the code; more efficient when used as constants.

[Encapsulation: the function is self contained.]

Code layout [Modularisation]:

• Complex operations should be broken up into subroutines that are defined separately and called from the main routine.
• Modularisation is easier if the program has been designed using top-down techniques.

Code layout [Indentation]:

• Code within structures should be inherited.
• White spaced should run from start to end of statement.
• Makes it clear where structures are nested.

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