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Do while loops check the condition after the block of code is executed. This control structure can be known as a post-test loop. This means the do-while loop is an exit-condition loop. However a while loop will test the condition before the code within the block is executed.
The condition/expression is evaluated, and if the condition/expression is true, [1] the code within all of their following in the block is executed. This repeats until the condition/expression becomes false. Because the while loop checks the condition/expression before the block is executed, the control structure is often also known as a pre ...
The following example is done in Ada which supports both early exit from loops and loops with test in the middle. Both features are very similar and comparing both code snippets will show the difference: early exit must be combined with an if statement while a condition in the middle is a self-contained construct.
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.
For example, instead of testing whether x equals 1.1, one might test whether (x <= 1.0), or (x < 1.1), either of which would be certain to exit after a finite number of iterations. Another way to fix this particular example would be to use an integer as a loop index , counting the number of iterations that have been performed.
The language permits counted loops, where an expression is computed at the start of the loop and the instructions within the loop are executed that many times: do expression [instructions] end. The language supports an unconditional loop via forever that continues until the loop is aborted or the program is terminated. do forever [instructions] end
for i := 1 : N while A(i) > 0 do etc. That is, a value is assigned to the loop variable i and only if the while expression is true will the loop body be executed. If the result were false the for-loop's execution stops short.
In software engineering, a spinlock is a lock that causes a thread trying to acquire it to simply wait in a loop ("spin") while repeatedly checking whether the lock is available. Since the thread remains active but is not performing a useful task, the use of such a lock is a kind of busy waiting .