I received an email question recently about the power of the break keyword. The answer to the question is that you can only break out of the current loop or switch-case structure. Even in a nested loop, or a switch-case structure within a loop, break affects only the current element.
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The standard C library contains a clutch of functions you use all the time, such as printf(), getchar(), malloc(), time(), rand(), and others. If you look in the library, you may discover some oddball functions that you’ve never used. One of those oddball functions might be ungetc().
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In last week’s Lesson, I demonstrated the strdup() function. That function isn’t available in every C language library, but it’s easy to craft your own.
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The C library function to copy a string is strcpy(), which (I’m guessing) stands for string copy.
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This month’s Exercise involves coding the lyrics for a cumulative song. Perhaps the most famous, and certainly the most obnoxious, cumulative song is the old warhorse, 99 Bottles of Beer.
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The old computer processing adage is “garbage in, garbage out.” What it means is that unless your data is good, don’t expect to see good results. So what can be done to ensure that the data is good? A checksum, that’s what.
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The final part of the decoding program performs the actual decoding: A two-byte hexadecimal string is converted into a value. That value is then manipulated by the XOR 0xAA operation. The result is output. Yep, it took a long time to get to this point.
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Data encoded by my hexencode system is formatted. That means that the decoding program must look for both the header and footer in that formatted output. In last week’s Lesson, code was added to confirm the input file’s first line as the header. This week’s modification is to search for the end of encoded text.
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You don’t want your decoding program to waste time attempting to process input that isn’t in the proper format. That’s why the encoding program bothers to put a specific header as the first line of text. Therefore, one of the first tasks for the decoding program is to check for that specific header.
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It would be a grand thing to set out and craft the entire decoding program in one sitting. That’s ambition in action, but it doesn’t demonstrate much programming experience.
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