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In computer programming languages, a switch statement is a type of selection control mechanism used to allow the value of a variable or expression to change the control flow of program execution via search and map. Switch statements function somewhat similarly to the if statement used in programming languages like C/C++, C#, Visual Basic .NET ...
Duff realized that to handle cases where count is not divisible by eight, the assembly programmer's technique of jumping into the loop body could be implemented by interlacing the structures of a switch statement and a loop, putting the switch's case labels at the points of the loop body that correspond to the remainder of count/8: [1]
Examples of, and arguments for, Jump Tables via Function Pointer Arrays in C/C++; Example code generated by 'Switch/Case' branch table in C, versus IF/ELSE. Example code generated for array indexing if structure size is divisible by powers of 2 or otherwise. "Arrays of Pointers to Functions" by Nigel Jones
Switch statements can allow compiler optimizations, such as lookup tables. In dynamic languages, the cases may not be limited to constant expressions, and might extend to pattern matching, as in the shell script example on the right, where the *) implements the default case as a glob matching any string.
Multiway branch is the change to a program's control flow based upon a value matching a selected criteria. It is a form of conditional statement.A multiway branch is often the most efficient method of passing control to one of a set of program labels, especially if an index has been created beforehand from the raw data.
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.
A loop-switch sequence [1] (also known as the for-case paradigm [2] or Anti-Duff's Device) is a programming antipattern where a clear set of steps is implemented as a switch-within-a-loop. The loop-switch sequence is a specific derivative of spaghetti code .
Many compound statements are loop commands or choice commands. In theory only one of each of these types of commands is required. In practice there are various special cases which occur quite often; these may make a program easier to understand, may make programming easier, and can often be implemented much more efficiently.