CS242N Lecture 4 Adam Mitz mitzcse.wustl.edu Dept. of Computer Science and Engineering Washington Un

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CS242N Lecture 4Adam Mitz (mitz_at_cse.wustl.edu)
Dept. of Computer Science and EngineeringWashingt
on University in St. Louis

• Style
• Tips for Good Code
• 242 Conclusions

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Style Goals

• Optimize for programmer time, not execution time.
• Easy to read (for you and others)
• Easy to debug
• Easy to re-use code in future projects
• Consistency among programmers
• You may think you know what the execution time
  will be, but you dont!
• Algorithms look like their pseudocode
• Make it easy to write correct syntax the first
  time through the compiler

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General Suggestions 1

• Heed compiler warnings
• Use encapsulation and good object-oriented design
  (methods do only what their name implies)
• Verify newly written procedures
• Step through with debugger, checking sanity of
  variable values and code coverage
• Write a testing routine (esp. for templates)
• Use representation invariants and asserts
• Avoid globals and nonmember statics

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General Suggestions 2

• Comment for readability, for others and yourself
  (you wont remember what you were thinking)
• Avoid pointer operations and new/delete when
  possible
• Always check array index bounds in DEBUG code
• Use each variable for exactly one purpose.
• Use a consistent layout and whitespace scheme

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Avoiding Pointers

• Object oriented programs can be written using
  references in many places where you may be
  tempted to use pointers.
• new returns a pointe, but you can convert the
  result from new into a reference with the
  operator
• Variables that may be NULL must be pointers
• Use an array class (template) instead of a native
  dynamic array
• Pass parameters and return values by reference
  (with const as appropriate)

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Style for Memory Management

• If a function calls new, clearly indicate in
  comments if the client must call delete (or
  some cleanup function that does) to avoid a leak.
• Example
• Matrix mult(Matrix m1, Matrix m2)
• // mult creates a new matrix, calling function
  must delete

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Textual Formatting

• Use white space to aid readability
• Between expressions and operands
• Blank lines between statement groups
• Split up complicated expressions into multiple
  statements (temporary const variable)
• Use descriptive identifier names for local
  variables, functions, classes, methods, etc
• Comments having too few or too many is bad.
  Dont comment obvious ideas that your code
  already conveys.

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Modified Hungarian Notation for Variable Names

• Scope Prefixes
• m_ class member
• g_ global
• s_ static
• in_ input to function
• out_ output parameter
• inout_ modified parameter
• (none) local

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Hungarian Continued

• Type Prefixes
• i int, c char, f float, d double
• p pointer, a array, o other
• Format
• ltscopegt_lttypegtlttypegtName
• Examples
• int m_aiIndicies10
• draw(const Point in_ptStart, )
• void length(double out_dLength)
• double g_dEpsilon 1e-6

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Conclusions

• Avoid the tendency to use code tricks it will
  make the code less readable
• Non-obvious syntax should be commented
• Use the debugger and assert
• Write testing functions that call all members
  especially for templates
• C requires you to think at a high level
  (classes, templates) and at a low level
  (pointers, bit manipulation) at the same time.
• C requires attention to detail in syntax, and
  thinking about how your program will behave at
  runtime.

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Course Info

• Email me questions any time
• Unix command to send in your homework
• cd 242 tar czvf - uuencode 242.tgz.uue
  Mail s 242 mitz_at_cse.wustl.edu
• Do so by a week from today
• Evaluations will be placed in your pendaflexes at
  the end of the semester

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Credits

• CS242N was developed by
• Prof. Bill Smart (wds_at_cse.wustl.edu)
• Prof. Cindy Grimm (cmg_at_cse.wustl.edu)