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These are called "Boolean" variables in reference to the notable 19th century mathematician George Boole. Boole's greatest work was entitled An Investigation of the Laws of Thought on Which Are Founded the Mathematical Theories of Logic and Probabilities, published in 1854. Boole reduced logic (the analysis of the truth or falsity of complex propositions) to a simple algebra, thereby incorporating logic into mathematics. Boole's two-valued, or binary, algebra is the simplest form of his more general boolean algebra.

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Technically, the result of applying a C logical operator is of the particular C numeric data type called int.

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Alcock rather misleadingly talks of certain characters being stored in a certain "order" and/or "contiguously"; what he means is that characters are encoded in a certain order or contiguously.

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Its actually even more complicated than this, but I will spare you any further details!

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This possibility is not pursued in detail by Alcock at this stage, but is raised implicitly in Exercise 4 of the chapter.

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Note that the names of separate variables must be textually different, even if only "slightly" so.

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The prototype for the exit() function is in the header file stdlib.h, so you should #include this header at the top of your file if you intend to use the exit() function.

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In particular, you might have a look at the standard library facilities for "process control" described in pagese 171-176 of Illustrating C - though this is not for the faint hearted!

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In general when I refer to the name of a function I include a pair of parentheses after the name, as in main(). I adopt this convention so that, whenever I use a name, you can easily tell whether it is intended as the name of a function or of a variable. In fact, the compiler works much the same way: when it sees a name in an expression, it looks to see whether the name is followed by a left parenthesis, and, if so, it knows that the name is supposed to refer to some function.

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I use the term "sub-function" loosely in this kind of context to distinguish between one "calling" function and a second function which is "called". However, "sub-function" is not a technical term of the C language: to C all functions are "equal" - there is no kind of precise distinction between "functions" and "sub-functions".

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Note that the function for printing out the result will not have to vary or be modified...

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A technical exception here is in the case of array arguments. C has some special rules for what happens when an array name is used in an expression (without any index) - such as when an array is specified as an argument. The nett effect is that arrays "sort of" get passed by reference: but the details of this are beyond the scope of the current discussion.

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Both printf() and scanf() are exceptions to this rule - they can deal with varying numbers of arguments. But this is highly exceptional: most of the library functions we deal with will only accept fixed numbers of arguments; and all of the user defined functions covered in this course will only accept fixed numbers of arguments.

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Again, printf() and scanf() are exceptions to this general rule; but also again, it is beyond the scope of this course to consider this very exceptional behaviour in any further detail!

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In some cases, the prototype for a particular function may be included in several different header files; in such a case you just have to insure that at least one of them is #include'd in your file.

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When I say that the name of the function is "replaced" by the returned value, I do not, of course, mean literally that the text of your program is altered. Rather I mean that the way to understand what happens next at execution time is to imagine the return value appearing in the place occupied by the function name.

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Other functions may be "active" - main() is active all the time, for example - but be temporarily suspended while a sub-function is executing. Their variables still exist, and will become visible again in the Watch window as execution returns to them...

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OK: this is a little white lie. It can be done, but only using the mechanisms of struct data types. This is beyond the scope of the current discussion, but have a browse in Chapter 8 of Illustrating C if you want to explore this further...

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If you manage this successfully, you should be able to see the new directory listed by File Manager - for example as D:MYDIR or whatever.

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You will have to "format" the diskettes first. Disk formatting and file copying and deleting operations are all carried out with the File Manager: again, consult the online help for details!

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Login as "opac".

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This will be DemoA, DemoB, DemoC or DemoD, where the last letter is the letter of your section in the class.

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Note that you can specify multiple recipients for a mail message by separating them by commas, and you can send mail to yourself, though it will not be visible until you exit Mail and re-enter it again.

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If you did not do this in advance - shame on you. Do it now!

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If this directory already exists you can leave it there, but delete all files and/or subdirectories which may be in it.

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I strongly discourage the use of multiple edit windows simultaneously accessing the same file: this usually ends in tears! In fact, at this stage in your programming education, you would do well to restrict yourself to a maximum of 3 simultaneous edit windows (even accessing different files), at any given time.

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A slightly more sophisticated, and convenient, alternative, is to display the Output window (select the Output menu item on the Window menu). This is a normal Turbo-C++ IDE window which can be moved around and resized etc., but which "mirrors" whatever output appears on the User Screen. Thus, it can allow you to still see the output even while the User Screen itself is not being displayed.

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Most people have a natural disinclination to be severe in testing their own work - but relish the thought of demonstrating the flaws in the work of somebody else. Sad but true - and, in this case, rather useful.

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The maximum size stipulated in the textbook is 100 by 100; but with the Turbo-C++ application, as currently configured, this is too large for it to handle. Hence the reduction to 50 by 50.

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You should have found that, if you click on the hot-linked file names, you can get a display of either of these files, within Mosaic. You can, of course, retype each program from this display into the Turbo-C++ IDE. However, you may also save the files directly from Mosaic, using the Save As menu item on the File menu. Which saves a bit of typing.

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If this still doesn't kill the program, then you will probably have to use the Reset button on the computer system unit, in order to reset the whole computer. But the reset procedure is quite slow, and, of course, you will lose any modifications to files which have not been saved to disk again. So this is a very last resort!

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This strategy might run into difficulty if we were concerned, for whatever reason, to only use as much memory as absolutely necessary. Fortunately, this does not apply to the current exercise.

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This is actually a very general point in C: anywhere a single statement can be legally used, then a whole set of statements, enclosed in braces, can be used instead.

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Be warned: when using scanf() to read values into a variable of type double, the correct format specification is %lf rather than %f; but, paradoxical as it seems, you should still use %f as the format specification for printing values of type double with printf().

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You should have found that, if you click on the hot-linked file name, you can get a display of the file, within Mosaic. You can, of course, retype the program from this display into the Turbo-C++ IDE. However, you may also save the file directly from Mosaic, using the Save As menu item on the File menu.

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Think carefully about the selection of test cases. For example do you expect there to be some biggest numbers for which the HCF() function will work? Smallest numbers? Should it work if either of the arguments is zero? Should it work for negative arguments? Does it matter which argument is given first - the bigger or the smaller? And so on...

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That is, using something like #define KEY 5, or const int key = 5. See page 34 of Illustrating C.

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Technically, under the various idealizing assumptions we have made, it can be shown that the trajectory will be parabolic.

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This change will, of course, be negative, because is negative; to put that another way, what goes up must come down!

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That is: both a and A should contribute to the count for the letter "a"; and non-alphabetics should not contribute to any count.

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LaTeX is a typesetting mark-up language, particularly suitable for hierarchically organised documents, and documents using mathematical notation extensively. It is a de-facto standard in academic publishing. A LaTeX source file is still a form of ASCII, but with typesetting commands interspersed with the "raw" text. It can be read with any tool which can display ASCII files.

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Alternatively, you might want to install a copy of the Programmer's File Editor. This is a powerful (and free!) professional text editor for Windows. It does the same job as NotePad, but much better!