Which loop is faster, while or for?

Solution 1:

That clearly depends on the particular implementation of the interpreter/compiler of the specific language.

That said, theoretically, any sane implementation is likely to be able to implement one in terms of the other if it was faster so the difference should be negligible at most.

_{Of course, I assumed while and for behave as they do in C and similar languages. You could create a language with completely different semantics for while and for}

Solution 2:

In C#, the For loop is slightly faster.

For loop average about 2.95 to 3.02 ms.

The While loop averaged about 3.05 to 3.37 ms.

Quick little console app to prove:

 class Program
    {
        static void Main(string[] args)
        {
            int max = 1000000000;
            Stopwatch stopWatch = new Stopwatch();

            if (args.Length == 1 && args[0].ToString() == "While")
            {
                Console.WriteLine("While Loop: ");
                stopWatch.Start();
                WhileLoop(max);
                stopWatch.Stop();
                DisplayElapsedTime(stopWatch.Elapsed);
            }
            else
            {
                Console.WriteLine("For Loop: ");
                stopWatch.Start();
                ForLoop(max);
                stopWatch.Stop();
                DisplayElapsedTime(stopWatch.Elapsed);
            }
        }

        private static void WhileLoop(int max)
        {
            int i = 0;
            while (i <= max)
            {
                //Console.WriteLine(i);
                i++;
            };
        }

        private static void ForLoop(int max)
        {
            for (int i = 0; i <= max; i++)
            {
                //Console.WriteLine(i);
            }
        }

        private static void DisplayElapsedTime(TimeSpan ts)
        {
            // Format and display the TimeSpan value.
            string elapsedTime = String.Format("{0:00}:{1:00}:{2:00}.{3:00}",
                ts.Hours, ts.Minutes, ts.Seconds,
                ts.Milliseconds / 10);
            Console.WriteLine(elapsedTime, "RunTime");
        }
    }