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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 ...
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. In contrast a "while" loop runs while the control expression is true and terminates once the expression becomes false.
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.
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.
If xxx1 is omitted, we get a loop with the test at the top (a traditional while loop). If xxx2 is omitted, we get a loop with the test at the bottom, equivalent to a do while loop in many languages. 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 ...
Infinite loops can be implemented using various control flow constructs. Most commonly, in unstructured programming this is jump back up , while in structured programming this is an indefinite loop (while loop) set to never end, either by omitting the condition or explicitly setting it to true, as while (true) ....
The majority of the most popular programming languages use reserved keywords. Early examples include FLOW-MATIC (1953) and COBOL (1959). Since 1970 other examples include Ada, C, C++, Java, and Pascal. The number of reserved words depends on the language: C has about 30 while COBOL has about 400.
for i from f by b to t while w do # loop body od; All parts except do and od are optional. The for I part, if present, must come first. The remaining parts (from f, by b, to t, while w) can appear in any order. Iterating over a container is done using this form of loop: for e in c while w do # loop body od;