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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.
Sometimes within the body of a loop there is a desire to skip the remainder of the loop body and continue with the next iteration of the loop. Some languages provide a statement such as continue (most languages), skip, [8] cycle (Fortran), or next (Perl and Ruby), which will do this. The effect is to prematurely terminate the innermost loop ...
A number of languages implement a form of switch statement in exception handling, where if an exception is raised in a block, a separate branch is chosen, depending on the exception. In some cases a default branch, if no exception is raised, is also present. An early example is Modula-3, which use the TRY...
In computer science, a for-loop or for loop is a control flow statement for specifying iteration. Specifically, a for-loop functions by running a section of code repeatedly until a certain condition has been satisfied. For-loops have two parts: a header and a body. The header defines the iteration and the body is the code executed once per ...
A block is a grouping of code that is treated collectively. Many block syntaxes can consist of any number of items (statements, expressions or other units of code) – including one or zero. Languages delimit a block in a variety of ways – some via marking text and others by relative formatting such as levels of indentation.
For example, a ranged loop like for x = 1 to 10 can be implemented as iteration through a generator, as in Python's for x in range(1, 10). Further, break can be implemented as sending finish to the generator and then using continue in the loop.
Thus the loop will always result in x = 2 and will never break. This could be fixed by moving the x = 1 instruction outside the loop so that its initial value is set only once. In some languages, programmer confusion about mathematical symbols may lead to an unintentional infinite loop. For example, here is a snippet in C:
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.