i plus plus

[k i r s t i n]

pluses for i++: you often want to start with an i of zero for the first
loop through if you're accessing elements at an index (with the exception
of matlab's indexing).  for (i=-1; i<10; ++i) is just plain awkward for
that.

-K

On Tue, 13 May 2003, David Lowenfels wrote:

> for( i=0; i<10; i++ ) {;}  //this is slow but very clear
>
> for( i=0; i<=10; ++i ) {;} //this is faster
>
> or if you don't need an index, just a repeat:
>
> i = 10+1; //loop 10 times... sorta confusing
> while( --i ) {;}	//this is fastest?
>
> I think maybe people use i++ becuase it is semantically simple... no
> weird extra number stuff.
>
> -DFL
>
> >You got it backwards again...
> >++i is faster than i++
> >
> >++i  is pre-assignment-increment, in other words increment and then
> >assign the value
> >i++ is post-assignment-increment, in other words assign the value
> >then increment.
> >
> >so that means every time you use post-increment a temporary variable
> >holding the present state of the variable is created so that it can
> >be returned and the actual value incremented, this is the semantic
> >definition and how it must be implemented in any class.
> >
> >as an example:
> >
> >++i
> >{
> >i = i + 1;
> >return i;
> >}
> >
> >and ...
> >
> >i++
> >{
> >int j = i;
> >i = i + 1;
> >return j;
> >}
> >
> >so....
> >
> >int i = 0;
> >cout << i++;
> >
> >output = 0
> >
> >and...
> >
> >int i = 0;
> >cout << ++i;
> >
> >output = 1;
> >
> >this behaviour only comes into play with assignments so since you
> >have the pick of the two in loops you should choose the faster one
> >which is always ++i. I have no idea why i++ is in every basic loops
> >example in every loop. I guess it must have been in a basic example
> >in the Kernigan-Ritchie book (the first book on C, by the authors of
> >C, also where that "Hello world!" example program now the standard
> >in ALL programming text books comes from!)
> >
> >jeffyb
> >
> >
> >
> >
> >Hiroko Terasawa wrote:
> >
> >>Thanks Jeffyb,
> >>
> >>
> >>>use ++i in loops instead of i++, it's pre-increment so it's faster
> >>>
> >>>
> >>I use i++ for coding, but when writing ...
> >>...snip...
> >>increment? Why does it make the code faster?
> >>
> >>ps. I found a treat for you...
> >>http://mirror.wolffelaar.nl/zardalu.sytes.net/
> >
> >_______________________________________________
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>
>
> --
> _/^\_/^\_/^\_/^\_/^\    Science is but a perversion of itself unless
>    David Lowenfels       it has as its ultimate goal the betterment
>   Vibrational Engineer   of humanity. -- Nikola Tesla
> ^\_/^\_/^\_/^\_/^\_/^            http://www-ccrma.stanford.edu/~dfl/
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