What distinguishes a do..while loop from a while loop?

The distinction between a do..while loop and a while loop primarily lies in how and when the loop conditions are evaluated, which is fundamental to understanding their behavior in controlling the execution of code blocks.

A do..while loop guarantees that the block of code within it will be executed at least once before the condition is tested at the end of the loop iteration. This means that regardless of whether the condition evaluates to true or false, the code will run at least one time. In contrast, a while loop checks its condition before executing the loop's code. If the condition is false from the outset, the while loop's block may not execute at all.

Therefore, the assertion that a while loop may not execute at all accurately captures this key difference. In summary, the ability of a do..while loop to ensure that its body executes at least once demonstrates its unique function compared to a while loop, which may skip execution entirely if the initial condition is not met.