Pre- and post-increments

[SirFalcon]

Ok, so I read the related section at the Java site about Assignment, Arithmetic, and Unary Operators, but I honestly don't get the code they provide:

class PrePostDemo {
     public static void main(String[] args){
          int i = 3;
	  i++;
	  System.out.println(i);	// "4"
	  ++i;			   
	  System.out.println(i);	// "5"
	  System.out.println(++i);	// "6"
	  System.out.println(i++);	// "6"
	  System.out.println(i);	// "7"
     }
}

I understand that i++ adds 1 to the original value, and ++i adds 1 to the incremented value.

When i++ prints '6', does that mean the original value of i=3 is changed to 5 at this point?

I also don't get why i=7 at the end.

[Fubarable]

I understand that i++ adds 1 to the original value, and ++i adds 1 to the incremented value.

Do you have a book chapter on this? If so, you should re-read it as again your assumptions about your understanding is incorrect. Both i++ and ++i add to the original value. ++i adds to the int before it is used and i++ adds to it after it has been used. Again, this will probably be better explained in your book.

[SirFalcon]

The Java class I am taking unfortunately does not provide us with a book so I am stuck with Powerpoint slides that aren't really helpful. I might go out and buy a book I guess.

[Fubarable]

I might go out and buy a book I guess.

I would agree with this 100%. When I'm learning a new programming language, I usually go out and buy several books because it is tough getting these new concepts into my head. Many of the books I buy are used, so they're obtained on the cheap. Also, you should check out the Sun Java tutorials which are better than cheap -- they're free. You'll find them here: Sun Java Tutorial Big Index

The section on the incr and decr operators can be found here: operators

[SirFalcon]

I'll check out those links. And thank-you very much for your advice. :D

[Fubarable]

To go through your code:

     public static void main(String[] args){
          int i = 3;
	  i++;                                // add one to i
	  System.out.println(i);	// display this number
	  ++i;			        // add again to i
	  System.out.println(i);	// display this number
	  System.out.println(++i);	// first add one to i, THEN display it.
	  System.out.println(i++);	// first display i, THEN after it's been displayed, add one to it.
	  System.out.println(i);	// "7"
     }

[SirFalcon]

Makes perfect sense now! You have been a great help, thank-you.