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Duff's device provides a compact loop unrolling by using the case keyword both inside and outside the loop. This is unusual because the contents of a case statement are traditionally thought of as a block of code nested inside the case statement, and a reader would typically expect it to end before the next case statement.
Switch statements function somewhat similarly to the if statement used in programming languages like C/C++, C#, Visual Basic .NET, Java and exist in most high-level imperative programming languages such as Pascal, Ada, C/C++, C#, [1]: 374–375 Visual Basic .NET, Java, [2]: 157–167 and in many other types of language, using such keywords as ...
Switch statements (or case statements, or multiway branches) compare a given value with specified constants and take action according to the first constant to match. There is usually a provision for a default action ("else", "otherwise") to be taken if no match succeeds. Switch statements can allow compiler optimizations, such as lookup tables.
The switch parser function, coded as "#switch", selects the first matching branch in a list of choices, acting as a case statement. Each branch can be a value , an expression ( calculation ), or a template call, [ 1 ] evaluated and compared to match the value of the switch.
Bash reads constructs all at once, such as compound commands which include if-fi and case-esac blocks. If a set -v is included within a compound command, then "verbose" will be enabled the next time Bash reads code as input, ie, after the end of the currently executing construct. [ 108 ]
getopt is a system dependent function, and its behavior depends on the implementation in the C library. Some custom implementations like gnulib are available, however. [6]The conventional (POSIX and BSD) handling is that the options end when the first non-option argument is encountered, and that getopt would return -1 to signal that.
The loop-switch sequence is a specific derivative of spaghetti code. It is not necessarily an antipattern to use a switch statement within a loop—it is only considered incorrect when used to model a known sequence of steps. The most common example of the correct use of a switch within a loop is an inversion of control such as
Loops using while, repeat until or do, and for statements; switch a.k.a. case statements, a form of multiway branching; These new language mechanisms replaced equivalent flows which previously would have been written using gotos and ifs. Multi-way branching replaces the "computed goto" in which the instruction to jump to is determined ...