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Because the while loop checks the condition/expression before the block is executed, the control structure is often also known as a pre-test loop. Compare this with the do while loop, which tests the condition/expression after the loop has executed. For example, in the languages C, Java, C#, [2] Objective-C, and C++, (which use the same syntax ...
If while is omitted, we get an infinite loop. The construction here can be thought of as a do loop with the while check in the middle. Hence this single construction can replace several constructions in most programming languages. Languages lacking this construct generally emulate it using an equivalent infinite-loop-with-break idiom: while ...
Some CFG examples: (a) an if-then-else (b) a while loop (c) a natural loop with two exits, e.g. while with an if...break in the middle; non-structured but reducible (d) an irreducible CFG: a loop with two entry points, e.g. goto into a while or for loop A control-flow graph used by the Rust compiler to perform codegen.
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.
However, infinite loops can sometimes be used purposely, often with an exit from the loop built into the loop implementation for every computer language, but many share the same basic structure and/or concept. The While loop and the For loop are the two most common types of conditional loops in most programming languages.
The break statement is used to end a for loop, while loop, do loop, or switch statement. Control passes to the statement following the terminated statement. A function returns to its caller by the return statement. When return is followed by an expression, the value is returned to the caller as the value of the function.
For example, a break statement would allow termination of an infinite loop. Some languages may use a different naming convention for this type of loop. For example, the Pascal and Lua languages have a " repeat until " loop, which continues to run until the control expression is true and then terminates.
The following example demonstrates dynamic loop unrolling for a simple program written in C. Unlike the assembler example above, pointer/index arithmetic is still generated by the compiler in this example because a variable (i) is still used to address the array element.