Using equality in 'for' loop - why not?

[Mark Anderson]

A 'for' loop takes 3 arguments (initialize; test; increment). The 'test'
must equate as true or false

This doesn't work...
x = 5;
for (y=1; (y==5); y+=1) {
alert(x * y);
}
...nor does...
x = 5;
for (y=1; (y===5); y+=1) {
alert(x * y);
}
....but this does..
x = 5;
for (y=1; (y<6); y+=1) {
alert(x * y);
}

Why do the first two fail? If i is value 5 then i==5 is true, as is
i===5.

Can anyone explain what I'm missing here?

Regards

[Hywel]

In article <c9************ *******@news.de mon.co.uk>, Mark Anderson
says...

A 'for' loop takes 3 arguments (initialize; test; increment). The 'test'
must equate as true or false

This doesn't work...
x = 5;
for (y=1; (y==5); y+=1) {
alert(x * y);
}
This fails because after the first loop "y" becomes 12. Try
for (y=1; y!=5; y++)

Why do the first two fail? If i is value 5 then i==5 is true, as is
i===5.
The loop executes while the condition is true. In your example you
assign 1 to y, so the condition y==5 is false.

Can anyone explain what I'm missing here?

You're missing the documentation:
http://tinyurl.com/jbie

--
Hywel I do not eat quiche
http://kibo.org.uk/
http://kibo.org.uk/mfaq.php

[Erwin Moller]

Mark Anderson wrote:

Hi Mark

A 'for' loop takes 3 arguments (initialize; test; increment). The 'test'
must equate as true or false

This doesn't work...
x = 5;
for (y=1; (y==5); y+=1) {
alert(x * y);
}
yes, I think it works.
Just not as expected.
Your 'test' fails the first time because y=1 and not 5.

Think of for-loop as follows, maybe that helps:

for (initialize; test; increment){
statements;
}

is equal to:

initialize;
while(test) {
statements;
increment;
}
Now you can explain the rest too. :-)
..nor does...
x = 5;
for (y=1; (y===5); y+=1) {
alert(x * y);
}
...but this does..
x = 5;
for (y=1; (y<6); y+=1) {
alert(x * y);
}

Why do the first two fail? If i is value 5 then i==5 is true, as is
i===5.

Can anyone explain what I'm missing here?

Regards

Regards,
Erwin Moller

[Lee]

Mark Anderson said:

A 'for' loop takes 3 arguments (initialize; test; increment). The 'test'
must equate as true or false

This doesn't work...
x = 5;
for (y=1; (y==5); y+=1) {
alert(x * y);
}
..nor does...
x = 5;
for (y=1; (y===5); y+=1) {
alert(x * y);
}
...but this does..
x = 5;
for (y=1; (y<6); y+=1) {
alert(x * y);
}

Why do the first two fail? If i is value 5 then i==5 is true, as is
i===5.

Can anyone explain what I'm missing here?

You're setting x=5 and y=1 and seem to be surprised that y!=5.
Without knowing you, it's hard to guess whether this is oversight
or if you really are missing something.

[Stephen Chalmers]

"Hywel" <hy**********@h otmail.com> wrote in message
news:MP******** *************** *@news.individu al.net...

In article <c9************ *******@news.de mon.co.uk>, Mark Anderson
says...

A 'for' loop takes 3 arguments (initialize; test; increment). The 'test'
must equate as true or false

This doesn't work...
x = 5;
for (y=1; (y==5); y+=1) {
alert(x * y);
}

This fails because after the first loop "y" becomes 12.

Why is the first iteration performed and how does 'y' become 12?

--
S.C.

[Mick White]

Stephen Chalmers wrote:

Why is the first iteration performed and how does 'y' become 12?
x = 5;
for (y=1; y==5; y+=1) {
alert(x * y);
} S.C.

It doesn't.
The loop never starts, since y doesn't equal 5.

Mick

[Mark Anderson]

Lee

"Lee" <RE************ **@cox.net> wrote in message
news:c9******** *@drn.newsguy.c om...

Mark Anderson said:

A 'for' loop takes 3 arguments (initialize; test; increment). The 'test'must equate as true or false

This doesn't work...
x = 5;
for (y=1; (y==5); y+=1) {
alert(x * y);
}
..nor does...
x = 5;
for (y=1; (y===5); y+=1) {
alert(x * y);
}
...but this does..
x = 5;
for (y=1; (y<6); y+=1) {
alert(x * y);
}

Why do the first two fail? If i is value 5 then i==5 is true, as is
i===5.

Can anyone explain what I'm missing here?

Without knowing you, it's hard to guess whether this is oversight
or if you really are missing something.
You're setting x=5 and y=1 and seem to be surprised that y!=5.

And so I should be! I'm saying "start with y=1 ad while y is not 5
(ergo less than or equal to 5) do the loop and increment by five.

Your explanation is implying I'm testing in loop #1...

x = 5;
for (y=5; (y===5); etc...

I feel oppressed by all the right-brain thinking here.

Why didn't the blokes (perhaps ladies?) who wrote the spec just say
explicitly don't use ==/!=/===/!== in for loop test if they don't work.
I've looked at the NS docs - and there's no indication that these aren't
allowed.

Please folks I'm not an engineer or a logic PhD. Could posters please
*explain* their put-downs rather than just say you're wrong. I asked the
question both because I don't understand and I wish to understand why.
So far all that I've read is "I'm cleverer than you" answers telling me
I'm wrong. I know! Just please explain why...

Regards

Mark

[Klaus Johannes Rusch]

Mark Anderson wrote:

And so I should be! I'm saying "start with y=1 ad while y is not 5
(ergo less than or equal to 5) do the loop and increment by five.
You set y to 1 and then loop while y is equal to 5. Since y is not equal
to 5 before the first iteration, the loop body is never executed.
Why didn't the blokes (perhaps ladies?) who wrote the spec just say
explicitly don't use ==/!=/===/!== in for loop test if they don't work.
I've looked at the NS docs - and there's no indication that these aren't
allowed.

They are allowed, and there are cases where they make sense, for example

for (counter = 0; stillrunning == 1; counter++) {
if (something) stillrunning = 0;
}

The condition can be more complex, too -- in any case the way the loop
is processed is such that the condition is checked *before* executing
the loop, so if your condition is not true to start with, the loop is
executed zero times.

Hope that helps

--
Klaus Johannes Rusch
Kl********@atme dia.net
http://www.atmedia.net/KlausRusch/

[Evertjan.]

Mark Anderson wrote on 28 mei 2004 in comp.lang.javas cript:

This doesn't work...
x = 5;
for (y=1; (y==5); y+=1) {
alert(x * y);
}
Yes it works

start with y=1
then do something WHILE y==5

WHICH boolean is not true from the start,
so no alert output !!!
..nor does...
x = 5;
for (y=1; (y===5); y+=1) {
alert(x * y);
}
Yes it works

start with y=1
then do something WHILE y===5

WHICH boolean is NOT true from the start,
so no alert output !!!
...but this does..
x = 5;
for (y=1; (y<6); y+=1) {
alert(x * y);
}

Yes it surely works

start with y=1
then do something WHILE y<6

WHICH boolean is true when y=1, 2, 3, 4, 5

So 5 times an alert output

=============== =====

btw:
1 the () around y<6 are not needed
2 y+=1 is the same as y++
3 alerts in a loop can drive you crazy
4 using var can sometimes save you trouble when in a function,
because it leaves global values alone

Commonly this is used:

var x = 5;
for (var y=1; y<6; y++) {
document.write( x*y + "<br>");
}
--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

[Evertjan.]

Klaus Johannes Rusch wrote on 28 mei 2004 in comp.lang.javas cript:

They are allowed, and there are cases where they make sense, for example

for (counter = 0; stillrunning == 1; counter++) {
if (something) stillrunning = 0;
}

No, no sense, but this does:

var stillrunning = 17
for (counter = 0; stillrunning == 1; counter++) {
if (counter==2300 or somethingelse) stillrunning = 1;
}

though I would prefer:

var stillrunning = true
for (counter = 0; stillrunning ; counter++) {
if (counter==2301 or somethingelse) stillrunning = false;
}
--
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)