Today I stumbled upon the following article. I encourage you to read the article, but for brevity I will sum it up. Basically, when creating a for loop in most C-based languages, there are two basic incrementation operators: Pre-increment (++i) and Post-increment (i++), with Post-increment being by far more common. From a functional standpoint, in C# they are equivalent within a loop and always produce the same output. The premise of the article is that while Post-incrementing is recommended by most computer science professors, due to it’s implementation in the ECMA standards it is actually slower than Pre-incrementation.
I tend to be a skeptic, so when I read the article I thought the author must have been mistaken. After all, I assumed that computer science is a field where something as common as the for loop would be well documented and understood by the academics. In order to test the author’s claim I decided to write some code to test how long it took each operator to iterate 1 billion times incrementing a variable on each iteration. Here is the code:
using System;
namespace PostIncrementTest {
class Program {
static void Main(string[] args) {
const long reps = 1000000000;
for (int k = 0; k < 10; k++) {
long temp = 0;
// Define start time
DateTime firstLoopStart = DateTime.Now;
// Do a Post-Increment Loop
for (long i = 0; i < reps; i++) {
temp++;
}
// Define end time
DateTime firstLoopEnd = DateTime.Now;
temp = 0;
// Define start time
DateTime secondLoopStart = DateTime.Now;
// Do a Pre-Increment Loop
for (long i = 0; i < reps; ++i) {
++temp;
}
// Define end time
DateTime secondLoopEnd = DateTime.Now;
TimeSpan firstLoopTime = firstLoopEnd - firstLoopStart;
TimeSpan secondLoopTime = secondLoopEnd - secondLoopStart;
Console.WriteLine("The post-increment loop took {0} seconds", firstLoopTime.TotalSeconds);
Console.WriteLine("The pre-increment loop took {0} seconds", secondLoopTime.TotalSeconds);
}
// Show that the operators produce the same output
for(int i = 0; i < 10; i++)
{
Console.Write(i + " ");
}
Console.WriteLine();
for (int i = 0; i < 10; i++) {
Console.Write(i + " ");
}
Console.ReadLine();
}
}
}
And the results:
While there is a measurable difference between the two operators, it is so minute that over the course of 1 billion iterations it only amounted to .02 seconds difference on average on my machine. In a loop used in an every day program, this would most likely make no measurable difference. Although the difference was minute, I may still start using the Pre-increment operator since it is such a small change.
