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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 ...
In the C programming language, Duff's device is a way of manually implementing loop unrolling by interleaving two syntactic constructs of C: the do-while loop and a switch statement. Its discovery is credited to Tom Duff in November 1983, when Duff was working for Lucasfilm and used it to speed up a real-time animation program.
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.
However, for many uses of the switch statement in real code, it is possible to avoid branching altogether and replace the switch with one or more table look-ups. For example, the Has30Days example [presented earlier] can be implemented as the following:[C example]" "A Superoptimizer Analysis of Multiway Branch Code Generation" by Roger Anthony ...
Examples of, and arguments for, Jump Tables via Function Pointer Arrays in C/C++ [3] Example code generated by 'Switch/Case' branch table in C, versus IF/ELSE. [4] Example code generated for array indexing if structure size is divisible by powers of 2 or otherwise.
When a switch statement is reached, program execution continues with the statement after the case label with value that matches the value in the parentheses of the switch. If there is no such case label, but there is a default label, program execution continues with the statement after the default label.
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 combination of state variables and structured control, notably an overall switch statement, can allow a subroutine to resume execution at an arbitrary point on subsequent calls, and is a structured alternative to goto statements in the absence of coroutines; this is a common idiom in C, for example.