I recently had a reader submit a question regarding input. He wanted to write code that would read a character and display that character’s ASCII code value. It sounds like a simple program, but you must understand variable types and the scanf() function’s peculiarities to properly code it.
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The typical first program taught to anyone learning C (or any other programming language) is Hello, world! It’s fun, which sets up false expectations, but it’s also genius.
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When I recently researched byte-flipping on the Internet, I was surprised that the solution I used back in the 1980s wasn’t listed among the top solutions available today. That’s probably because my brain thinks like an Assembly Language programmer, so I crafted a low-level solution.
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Implementing a written algorithm is something you do frequently as a C language programmer. You’re given a set of directions and your job is to translate that English into computer code — and make that code work.
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One of the first programming puzzles I solved on my own was a byte flip. That’s the process for taking a binary value and flipping it: You transpose bits 0 through 7 to bits 7 through 0. This is a puzzle that comes up frequently in programming, but one for which no single solution is preferred.
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When you type a credit card number on a website, or scan the card into a physical device, a quick calculation is performed to ensure that the card number is valid. This check happens before the bank is contacted to verify the account and the amount. The technique used to perform the quick calculation is known as the MOD 10 algorithm.
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As an example of how a binary values can hold fractions, I’ve concocted a simple real number format: An 8-bit value with 4 bits representing the whole number portion and 4 bits representing the fractional portion. Here’s how it looks:
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Over the past few weeks, I’ve covered the concept of negative integers and their representation as binary values. What can also be represented in binary, something that’s even less obvious than negative values, are fractions.
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The far left bit in a signed integer value — no matter how wide the integer — is the sign bit. If it’s set, the value is negative. Otherwise, the value is positive. But the sign bit is more than just a minus sign. It also plays into binary math.
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In the C language, you have several ways to create a negative integer: You can assign a negative value to a variable, you can perform math that results in a negative value, or you can manipulate bits to convert a positive value to a negative one. That final operation isn’t as easy as it sounds.
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