It’s common in programming to use a factorial as a way to teach about recursion. For example, 5! (five factorial) is 5×4×3×2×1, which is 120. Calculating this result can be done with a recursive function, which is practical and satisfying. But mathematicians have a twisted sense of humor, so they invented something called a double factorial.
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I remember memorizing the “times tables,” which is how most American kids learn to multiply. Committing single digit multiplication values to memory helps perform multiplication and division problems, but it’s not the only way to calculate the result.
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The task for last month’s Exercise was to describe complex data — a matrix. For this month’s Exercise, your task is to multiply these matrixes.
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I’ve written many C programming Lessons and Exercises that deal with matrixes. For most of them, such as rotating a matrix, I rely on uniform matrix sizes, like 5×5 or 10×10. This approach makes coding easier, but it doesn’t properly describe every type of matrix.
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For me, the scariest part of learning how to program a computer was file access. The problem was the horrid documentation. It introduced both sequential and random file access together without much explanation. So it was with much trepidation that I wrote my first file I/O program. That’s when I realized that the manual was stupid.
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If you’ve studied the terminal window at any length, you probably know about the clear command, which clears the screen. Under MS-DOS, and on my old TRS-80, the command is cls. Same thing.
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Adding values is a basic programming concept: 4 + 5 = 9 But where do the values come from? They can be literals, variables, expressions, or values collected from the user.
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Even when statistics has barely brushed by you on the subway, you probably know the term standard deviation. It refers to how data is distributed in a group, their distance from the mean. You can use your C programming kung fu to code the standard deviation of a data set, which is the challenge for this month’s Exercise.
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I started my technology writing career at a computer book publishing house, CompuSoft. It’s no longer around, but I do recall ghost writing books such as the BASIC Handbook, which was an encyclopedia of the BASIC programming language. The first command listed in this book was ABS.
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Calculating a factorial is a common programming exercise, often coupled with introducing the concept of recursion. Mathematically, the factorial has a twin: the subfactorial. Its calculation can be a fun programming challenge, which is the subject of this month’s Exercise.
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