Which loop is guaranteed to execute at least once?

Which loop is guaranteed to execute at least once?

• A. for
• B. do-while
• C. while
• D. foreach

Answer: (B)

The loop type that ensures the body runs at least once is a post-test loop: you execute the body first, then check the condition to decide whether to continue. In the do-while structure, the flow is do { ... } while (condition); the body executes, and only afterward is the condition evaluated. If the condition is false on the first check, the loop stops, but the body has already run once. This is different from pre-test loops like while and for, where the condition is checked before any iteration, so the loop can do zero executions if the initial condition isn’t met. A foreach depends on the collection to iterate, so it can also produce zero iterations if the collection is empty. Therefore, the do-while construct is the one that guarantees at least one execution. Use it when you must perform an action at least once, such as prompting a user for input and continuing to prompt until a valid response is received.

The loop type that ensures the body runs at least once is a post-test loop: you execute the body first, then check the condition to decide whether to continue. In the do-while structure, the flow is do { ... } while (condition); the body executes, and only afterward is the condition evaluated. If the condition is false on the first check, the loop stops, but the body has already run once.

This is different from pre-test loops like while and for, where the condition is checked before any iteration, so the loop can do zero executions if the initial condition isn’t met. A foreach depends on the collection to iterate, so it can also produce zero iterations if the collection is empty. Therefore, the do-while construct is the one that guarantees at least one execution.

Use it when you must perform an action at least once, such as prompting a user for input and continuing to prompt until a valid response is received.