I don’t think I’ve ever used the return value from a printf() statement. Yes, the function has an int return value, which is the number of characters output. This value can be difficult to guess.
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In C programming, variables declared within a function are local to the function. Specifically, they’re the auto storage class, the default. External, or global, variables are defined outside of a function declaration and are of the extern storage class. These variables are available to all functions. But the scope within a function can also be limited, depending on where the variable is declared.
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As I wrote in last week’s Lesson, the system() function can’t be used in Linux to obtain a program’s return value. Instead, you must use one of the execl() family of functions. Further, this function must be spawned as a child process. This task involves using the fork() and wait() functions.
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The challenge for this month’s Exercise is to write a microwave oven input routine: The user types in a given number of seconds and your program translates the value into the proper number of hours, minutes, and seconds. This type of problem may sound familiar.
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At the end of the main() function, a return statement must surrender an integer value to the operating system. Does a higher value please the OS? Is it offended by zero? What exactly happens with the value returned when your program is done?
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I have a smart microwave oven. Say I need to heat my tea for a minute and a half. I type in 90. When I press the Start button, the 90 transforms into 1:30, a minute thirty. It’s the same quantity of time, but expressed differently. Such magic is merely clever programming.
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I screwed up some code in a most delightful manner, all without knowing what I did. In fact, it was a student who ran my less-than-brilliant code and discovered the obvious flaw. But I was clueless.
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The strcasecmp() function isn’t part of the standard C library, though many compilers feature it. As having the function is handy, I wrote about crafting your own version back in 2019. Alas, that implementation is flawed.
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Any mortal programmer would have stopped with last week’s Lesson, where a tally of unique and duplicate words is output. This is the desired result, right? Yes, but it’s an un-orderly list.
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Encoding means nothing if you can’t decode, which is the task for this month’s Exercise: Transform the encoded hex bytes back into characters, unwinding the formula used to create them. The challenge isn’t really as much with coding the math as it is with translating hex bytes back into integer values — characters.
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