The (Coding) Commands According to Dr. Bergeron

In my first semester at grad school (wow, now 18 years ago... I'm old), all CS master's students were required to take two intensive “this is what you should have learned during undergrad classes”, CS801 (theory) and CS802 (practice). The latter was taught by Dr. Dan Bergeron, who was — and probably still is — an excellent teacher, but whom I remember most as a man of stellar integrity and fairness — a good father-figure that most collegiate environments lack.

Anyway, while rummaging around some old papers the other day, I found this handout on “coding commandments” from the class. (It seems that programming in the class was done in Pascal — ugh.) The commandments are still as relevant today as then (well, perhaps the last one is more “advice” than “commandment”, and about some others, I do remember bristling at some of them, but I no longer remember which.)

I thought some of you might enjoy this, so pass it along...

Coding Commandments
CS802 - Fall 1987
October 30, 1987

The programming style conventions listed below shall be followed for programs submitted in this course. I firmly believe programs that follow these guidelines are more readable, more comprehensible and more maintainable than programs that do not follow the conventions. Furthermore, these conventions are consistent with well-established philosophies that define what constitutes good software engineering and are not just my idiosyncrasies (in spite of the fact that lots of existing software does not follow these guidelines). Finally, I will be the last to claim that there are no circumstances in which these guidelines should be violated. (In this course, however, there will be no exceptions!)


Every procedure/function shall have exactly 1 return statement and that statement will appear at the bottom of the procedure as the last executable statement of the procedure.


Every identifier used in the program shall have an associated comment that describes what the function of the identifier is. This includes symbolic constants, types, fields in records, parameters, variables, etc.


Every procedure/function shall be preceded by a clear separator (such as a row of asterisks or dashes or whatever) with a clear indication of the procedure name and a brief comment describing the essential function provided by that function.


A long procedure is a bad procedure. All the code for a procedure should fit on no more than one page, so that it can be readily comprehended by a reader.


Indentation of code is a very important tool in producing understandable code in which the control flow is readily discernible. Use good indentation that clearly shows the control flow. Don't let comments or debugging code obscure the indentation. Don't indent more than 2-4 blanks per nesting level.


Use a blank line to clearly identify major loop or conditional statements. A brief comment at the end of the line with the statement keyword is also very helpful if it tells at a high level what the statement does. If you have a loop or conditional that covers more than 8 lines or so, make sure that the end statement includes a comment that identifies which statement is being ended. If there are nested statements of the same type, be sure to include enough information to clearly identify the right one. (For example, end { while i <> 0 })


If you have an if-then-else statement with 1 short alternative and one long alternative, arrange the condition so that the short alternative is the then clause, and the long one is the else.


Use nested else-if in preference to nested then-if.


Every loop should have exactly one exit. Do not use a loop statement if a while or repeat is what you mean.


Use meaningful variable names.


Use symbolic constants excessively.


If you use arrays, you must always check the index for exceeding the bounds before trying to access the array element indicated by the index.


If you use lists, use a dummy sentinel, so that no list is ever empty. Generally, it is also wise to always have a tail pointer for efficiency of search and addition to the list. For searching, store the key you wish to search for in the tail (which is the sentinel), so that you are guaranteed to find it. Finally, if you are bothering to implement a list at all, you might as well implement two-way lists. The extra overhead of having the back pointer is insignificant and it makes deletion much easier.

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