Entrycontrolled

Entrycontrolled, also written as entry-controlled, refers to a class of loop constructs in programming where the loop condition is evaluated before each execution of the loop body. If the condition is false on the initial check, the loop may not execute at all. This contrasts with exit-controlled loops, where the loop body is executed first and the condition is tested after the body completes.

Common examples of entry-controlled loops are while loops and for loops in many programming languages. In a while loop, the condition is tested prior to entering the first iteration and before every subsequent iteration. In a typical for loop, initialization occurs first, then the condition is checked before each pass through the loop body; the loop may execute zero or more times depending on the condition and iteration step.

Exit-controlled loops, such as do-while loops, test their condition after the first execution of the loop body, guaranteeing at least one execution regardless of the condition.

Entry-controlled loops are often chosen when it is possible that the loop body should not run at all if the initial state does not meet the condition, or when the number of iterations is determined by the condition itself. However, they require careful handling to avoid infinite loops or off-by-one errors, particularly when the loop variable is updated inside the body.

In practice, many languages classify for, while, and similar constructs as entry-controlled, while do-while constructs belong to exit-controlled families. See also: pre-test versus post-test loops, loop termination, and loop invariants.