Question

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What is more efficient i++ or ++i?

No difference between these:

i++;
++i;

But when using them like this:

anArray[ i++ ] = 0;
anArray[ ++i ] = 0;

Is there a difference?

TO BE EDITED:
Thanks

Answer 1

Yes! Big difference!

i++ increments i after the line of code is executed expression is evaluated. ++i increments it before. For example:

int i = 2;
printf("%i\n", i++); //prints "2"
printf("%i\n", i);   //prints "3"

Compare with:

int i = 2;
printf("%i\n", ++i); //prints "3"
printf("%i\n", i);   //prints "3"

And I’ve heard that ++i is ever so slightly faster. Here is more on that.

Hope this helps!

UPDATE 2: Killed the last update, since the code technically had undefined behaviour. Moral of that story: Don’t use foo(i, ++i), foo(++i, ++i), foo(i++, i), etc. Or even array[i] = ++i. You don’t know what order the expressions get evaluated in!