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breaks, stops, and ends

summary

    This subchapter looks at breaks, stops, and ends.

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stub section

    This subchapter is a stub section. It will be filled in with instructional material later. For now it serves the purpose of a place holder for the order of instruction.

    Professors are invited to give feedback on both the proposed contents and the propsed order of this text book. Send commentary to Milo, PO Box 1361, Tustin, California, 92781, USA.

breaks, stops, and ends

    This subchapter looks at breaks, stops, and ends.

breaking loops

    So far we have gone through all loops for the complete set of iterations. What happens if we need to leave a loop early? Many academians would argue that we should have put all terminal conditions into our loop limits and that it is bad programming practice to escape from a control structure otherwise. And there is a strong argument that it makes it far easier to maintain the program over decades if the hard control structure rule is always followed. If for no other reason, another programmer doesn’t need to search for any special cases and exceptions.

    Even if we agree that you will never vioolate the sanctity of loops (at least while you are doing class assignments), you need to be aware of these contructs just so you can follow and fix other people’s code.

C

normal end

    The normal end of a program is the last statement of the highest level (main) program, procedure, or block.

    In most languages this is marked by the word end. The final end may or may not be followed a special character (such as a period or semicolon).

Pascal

abnormal end

    An abnormal end is any time a program ends or stops before the normal end.

    If this occurs unexpectedly at runtime it might be experienced by the end user as a crash or freeze. Obscure error messages may or may not be displayed.

    Some languages have the feature for a more controlled end,

    There are unrecoverable conditions a programmer can predict in advance.

    For example, the programmer might do error checking to determine if a key file exists and is properly formatted. If the required file is missing or broken, then obviously the program can not perform its expected work.

    Rather than simply crash, the programmer can escape out of the entire program, gracefully closing files and releasing resources.

    It would be a good idea to also report the problem in a way that the human end user can understand (remembering that your human end user may not be a programmer or even a technical skilled person).

PL/I

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