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The repeat statement repetitively executes a block of one or more statements through an until statement and continues repeating unless the condition is false. The main difference between the two is the while loop may execute zero times if the condition is initially false, the repeat-until loop always executes at least once.
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.
a b c Deep breaks may be accomplished in APL, C, C++ and C# through the use of labels and gotos. a Iteration over objects was added in PHP 5. a b c A counting loop can be simulated by iterating over an incrementing list or generator, for instance, Python's range() .
Then the condition is evaluated. If the condition is true the code within the block is executed again. This repeats until the condition becomes false. 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.
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.
Flow diagram a C-style for loop, representing the following code: for(i=0;i<5;i++) printf("*"); The loop will cause five asterisks to be printed. Flowcharts are used to design and document simple processes or programs.
Nassi–Shneiderman diagrams are only rarely used for formal programming. Their abstraction level is close to structured program code and modifications require the whole diagram to be redrawn, but graphic editors removed that limitation. They clarify algorithms and high-level designs, which make them useful in teaching.
SFC is an inherently parallel programming language in that multiple control flows — Program Organization Units (POUs) in the standard's parlance — can be active at once. Non-standard extensions to the language include macroactions: i.e. actions inside a program unit that influence the state of another program unit.