B# .NET Blog

I told you guys it was trivial :-). First of all, there's nothing wrong with the code:

 1 class Weird
 2 {
 3    static void Main()
 4    {
 5       int i = 1;
 6       for (i = 0; i < 100; i++)
 7       {
 8          System.Console.Write('.');
 9       } while (i <= 100);
10    }
11 }

Why? C# doesn't care about spacing; it could have written this as well:

1 class Weird { static void Main() { int i = 1; for (i = 0; i < 100; i++) { System.Console.Write('.'); } while (i <= 100); } }

Or - the more familiar form:

 1 class Weird
 2 {
 3    static void Main()
 4    {
 5       int i = 1;
 6       for (i = 0; i < 100; i++)
 7       {
 8          System.Console.Write('.');
 9       }
10       while (i <= 100);
11    }
12 }

The funny thing about it is the way it was created, but turning a do...while-loop into a for-loop without paying attention of the while portion. Actually, it had a totally different form which was a bit too heavy to put in here as a simple quiz. Originally, the loop termination condition was some boolean ok value that represents a test result of one single execution, do-whiling till the test fails at some random input - it was turned into a do-it-100-times kind of loop, so I ended up with some mixing of the following form:

bool ok;

for (int i = 0; i < 100; i++)
{
   //create some random input "someinput"
   ok = Foo(someinput);
} while (ok);

This reflects the fact that both loop constructs have a totally different set of characteristics when it comes down to the use of loop condition variables and the overall structure. In this context, did you know there's a subtle difference between the two (wrong!) fragments below:

class Loops
{
   static void Main()
   {
      for (int i = 0; i < 100; i++);
      {
         System.Console.Write(".");
      };
   }
}

class Loops
{
   static void Main()
   {
      for (int i = 0; i < 100; i++);;
      {
         System.Console.Write(".");
      };
   }
}

The result? One dot on the screen. At compilation? One warning in fragment one, no warning in fragment two. This might better deserve the nominator "weird".

To conclude, I like Eber's summary of an "optical illusion" because that's exactly what it is. In this case, a kind of philosophical question is: "why is do...while (condition) terminated with a semicolon?" (as soon as the do part disappears, you end up with an infinite loop after all). Another typical optical illusion is this one:

1 int x = 18;
2 if (x > 16)
3    if (x > 18)
4       Console.WriteLine("More than 18");
5 else
6    Console.WriteLine("Less than or equal to 16");

What will be printed on the screen? No rocket science, but coding style does matter!