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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One of my pastimes is watching math videos. I was a terrible math student, but I enjoy the videos. Occasionally a concept is presented that I can program in C. This month’s Exercise covers one of these concepts.
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Swapping values is common task in computer programming, often used when sorting. You need the value of variable a in variable b and vice-versa. A number of methods are available for swapping, most of which involve using a temporary variable to hold one of the values during the swap.
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Tetration is a mathematical process that generates obnoxiously huge numbers quickly. It’s exponentiation on overdrive. The concept is insane, but it’s also something you can code in C.
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I’m sure some eccentric term exists to describe a number where no digits repeat. Whether this concept has any mathematical relevance remains uncertain. But it’s the type of problem you can easily solve by writing a computer program.
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Probability. Odds. These are words I often confuse, but the similarity relates to how often things happen. The gold standard is the flip of a coin: two possibilities, heads or tails. If you don’t understand how it works, you can write code to drive home the point.
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When I was working on last month’s Exercise, I scoured the C library for a function that returned the number of specific characters found in a string. The closest I could find was strchr(), which returns the location of a given character in a string. You can set this function in a loop to find subsequent characters, but what I needed was a tally, a total count of all matching characters in the string.
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The Great Coding Wars host many battles. For example, VIM versus Emacs (add in Nano for extra military action). Also the fight between spaces and tabs for indenting. Add to these conflicts a minor skirmish: whether to use camelCase or snake_case naming conventions.
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Yes, this Exercise has been done before. But back then, exactly seven years ago, I had the digits reduced further so that the result was a single digit. This time, your goal is to tally the digits in an integer and report the results — no reductions!
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The classic paradigm for swapping values between two variables involves using a third variable. But is the third variable even necessary?
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