18. Special Considerations

This section contains some miscellaneous do's and don'ts.

• Don't change syntax via macro substitution. It makes the program unintelligible to all but the perpetrator.

• Don't use floating-point variables where discrete values are needed. Using a float for a loop counter is a great way to shoot yourself in the foot. Always test floating-point numbers as <= or >=, never use an exact comparison (== or !=).

• Compilers have bugs. Common trouble spots include structure assignment and bitfields. You cannot generally predict which bugs a compiler has. You could write a program that avoids all constructs that are known broken on all compilers. You won't be able to write anything useful, you might still encounter bugs, and the compiler might get fixed in the meanwhile. Thus, you should write "around" compiler bugs only when you are forced to use a particular buggy compiler.

• Do not rely on automatic beautifiers. The main person who benefits from good program style is the programmer him/herself, and especially in the early design of handwritten algorithms or pseudo-code. Automatic beautifiers can only be applied to complete, syntactically correct programs and hence are not available when the need for attention to white space and indentation is greatest. Programmers can do a better job of making clear the complete visual layout of a function or file, with the normal attention to detail of a careful programmer. (In other words, some of the visual layout is dictated by intent rather than syntax and beautifiers cannot read minds.) Sloppy programmers should learn to be careful programmers instead of relying on a beautifier to make their code readable.

• Accidental omission of the second "=" of the logical compare is a problem. Use explicit tests. Avoid assignment with implicit test.

  	abool = bbool;
  	if (abool) { ...
  

  When embedded assignment is used, make the test explicit so that it doesn't get "fixed" later.

  	while ((abool = bbool) != FALSE) { ...
  
  	while (abool = bbool) { ...	/* VALUSED */
  
  	while (abool = bbool, abool) { ...
  

• Explicitly comment variables that are changed out of the normal control flow, or other code that is likely to break during maintenance.

• Modern compilers will put variables in registers automatically. Use the register sparingly to indicate the variables that you think are most critical. In extreme cases, mark the 2-4 most critical values as register and mark the rest as REGISTER. The latter can be #defined to register on those machines with many registers.

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