The task is rather simple: Prompt the user to input a value between 1 and 9. If you’ve read the first few chapters of any of my For Dummies C programming books, you could do that one easily. But what happens when the user doesn’t type a value in that range or — worse — they type text instead?
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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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I crafted my solution to the cumulative song exercise by separating the parts of the song that are repeated from the unique text. Specifically, the ordinal days are unique as well as the gifts. The rest of the text is sung over and over.
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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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In my C programming books, I often use the directions on a shampoo bottle as an example of basic programming:
1. Lather.
2. Rinse.
3. Repeat.
Another real-life example of programming techniques happens in music. Specifically, cumulative songs are representative of loops. This type of song includes 99 Bottles of Beer and the holiday favorite, The Twelve Days of Christmas.
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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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