why does counter not stop?

[bob]

Hi,

Question about For (...).
I did this:
for (i=1;i=5;i++)
alert(i)

and i get an infinite loop with value '5'. I thought that 'i=5' was the test
which must be 'true' in order to execute 'alert(i)'. It's normal that i
don't get 1 to 4 because in those case, the test is false. When i=5, i get
alert(i) with 5 but appearantely, i never equals 6.

By the way, is there a difference between i++ and ++i? I tried both but
didn't find any difference.

Thanks
bob

[David Dorward]

bob wrote:

Question about For (...).
I did this:
for (i=1;i=5;i++)
alert(i)

and i get an infinite loop with value '5'. I thought that 'i=5' was the
test which must be 'true' in order to execute 'alert(i)'.
Two problems:

(1) The second parameter of the for loop has to be true to keep looping. It
will execute the content of block every time it loops.

(2) "=" is the assignment operator. The numerical test operator is "==".
It's normal that i don't get 1 to 4 because in those case
Nope. The first time round the loop you set i to 1, and then immediately
afterwards you set it to 5.
, the test is false.
i=5 is always true
When i=5, i get alert(i) with 5 but appearantely, i never equals 6.
Becuase you add one to it, and then set it back to 5 again.
By the way, is there a difference between i++ and ++i? I tried both but
didn't find any difference.

It's a case of when the increment happens.

<script type="text/javascript">
i = 0;
document.write (i +'<br>'+ i++ +'<br>'+ i +'<br>'+ ++i +'<br>'+ i);
</script>

might make things clear if you follow it through carefully.

--
David Dorward http://dorward.me.uk/

[bob]

thanks for replying
"David Dorward" <do*****@yahoo.com> wrote in message
news:bh******************@news.demon.co.uk...

bob wrote:

Question about For (...).
I did this:
for (i=1;i=5;i++)
alert(i)

and i get an infinite loop with value '5'. I thought that 'i=5' was the
test which must be 'true' in order to execute 'alert(i)'.
Two problems:

(1) The second parameter of the for loop has to be true to keep looping.

It will execute the content of block every time it loops.

(2) "=" is the assignment operator. The numerical test operator is "==".

It's normal that i don't get 1 to 4 because in those case

Nope. The first time round the loop you set i to 1, and then immediately
afterwards you set it to 5.

, the test is false.

i=5 is always true

When i=5, i get alert(i) with 5 but appearantely, i never equals 6.

Becuase you add one to it, and then set it back to 5 again.

By the way, is there a difference between i++ and ++i? I tried both but
didn't find any difference.

It's a case of when the increment happens.

<script type="text/javascript">
i = 0;
document.write (i +'<br>'+ i++ +'<br>'+ i +'<br>'+ ++i +'<br>'+ i);
</script>

might make things clear if you follow it through carefully.

--
David Dorward http://dorward.me.uk/