while loops

while loops allow you to execute a group of statements so long as a statment still evaluates to true.
Here's a quick example;

$num=20;
while($num<30){
   print "num is $num\n";
   $num=$num+1;
}

this will print out
num is 20
num is 21
...
num is 29
[download]

then num is incremented to 30 which is no longer less than 30 so the code within the while statement is not executed and execution jumps to the next statement outside of the while statement.

If you think you know all about while statements learn about his less popular brother until.

Edit Wed Aug 1 07:07:10 EDT 2001 - Petruchio Changed PRE tags to CODE tags, added whitespace.

Edit Mon Dec 02:27:42 EST 2004 - Petruchio changed '$while' to 'while', because this is in our Tutorials section, and should be accurate.

Comment on while loops Download Code

Replies are listed 'Best First'.
RE: while loops by Anonymous Monk on May 24, 2000 at 04:58 UTC
the $ before while should be deleted	[reply]
RE: while loops by IainB (Initiate) on Oct 27, 2000 at 16:31 UTC
I think something's missing from this description. It just doesn't look right to me.	[reply]
RE: RE: while loops by Albannach (Monsignor) on Oct 27, 2000 at 17:40 UTC
... nor me. There is definitely some data corruption.	[reply]
Re: RE: RE: while loops by Anonymous Monk on Jan 30, 2001 at 11:18 UTC
i think it should go like this $num = 20 ; while ($num < 30 ){ $num = $num + 10 ; }	[reply]
Re: Re: RE: RE: while loops by Anonymous Monk on Jun 06, 2001 at 15:33 UTC
Re: Re: RE: RE: while loops by Anonymous Monk on Mar 08, 2001 at 10:57 UTC
Re: while loops by rlivings (Acolyte) on Aug 01, 2001 at 14:02 UTC
initial example is still incorrect	[reply]
Re: Re: while loops by qwertydvorak (Initiate) on Aug 24, 2001 at 23:01 UTC
drop the $ before the while!	[reply]
Re: while loops by Glyndwr (Initiate) on Jan 11, 2002 at 18:35 UTC
Yours `$num=20; $while($num<30){ print "num is $num\n"; $num=$num+1;\n ; }` [download] should be `$num=20;<BR> while($num<30){ print "num is $num\n"; $num+=$num;\n; }` [download]	[reply] [d/l] [select]
Re: Re: while loops by rob_au (Abbot) on Jan 11, 2002 at 18:41 UTC
No, not at all - Your code will only pass through a single iteration of the loop as on the first pass, the value of `$num` is added to `$num`. The result is that `$num` equals `40` and the `while` loop is exited. I think you may have been meaning, ignoring formatting syntax errors ... `$num = 20; while ($num < 30) { print "num is $num\n"; ++$num; }` [download] Although, good pick up on the syntax error with the line - `$while($num<30){` - Although this had been addressed previously within this thread. `perl -e 's&&rob@cowsnet.com.au&&&split/[@.]/&&s&.com.&_&&&print'`	[reply] [d/l] [select]
Re: Re: Re: while loops by Glyndwr (Initiate) on Jan 11, 2002 at 19:11 UTC
yes , thanks in this case would $num++ also work	[reply]
Re^2: while loops by lvanhout (Curate) on Jun 15, 2004 at 17:42 UTC
Still not there. `$num=20; while($num<30) { print "num is $num\n"; <b><u>$num+=$num;\n</b></u> } #I think you ment: $num += 1; #Though these should work also: $num++; ++$num;` [download] There is also an extra "\n;" in the code in the reply.	[reply] [d/l]
Re: while loops by Anonymous Monk on Oct 21, 2004 at 04:31 UTC
I think the example code is bad. The correct code is `#!/usr/bin/perl $num=20; while ($num<30) { print "num is $num\n"; $num=$num+1; }` [download] Español El codigo que esta de ejemplo esta mal este es el correcto `#!/usr/bin/perl $num=20; while ($num<30) { print "num is $num\n"; $num=$num+1; }` [download] 20041020 Edit by ysth: use p, code, hr tags; fix tilde-n	[reply] [d/l] [select]


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