Editing Structured programming (section)

===Multiple entry===
{{further|Coroutine}}
More rarely, subprograms allow multiple ''entry.'' This is most commonly only ''re''-entry into a [[coroutine]] (or [[Generator (computer programming)|generator]]/semicoroutine), where a subprogram yields control (and possibly a value), but can then be resumed where it left off. There are a number of [[Coroutine#Common uses|common uses]] of such programming, notably for [[Stream (computing)|streams]] (particularly input/output), state machines, and concurrency. From a code execution point of view, yielding from a coroutine is closer to structured programming than returning from a subroutine, as the subprogram has not actually terminated, and will continue when called again – it is not an early exit. However, coroutines mean that multiple subprograms have execution state – rather than a single call stack of subroutines – and thus introduce a different form of complexity.

It is very rare for subprograms to allow entry to an arbitrary position in the subprogram, as in this case the program state (such as variable values) is uninitialized or ambiguous, and this is very similar to a goto.