""J. S. John"" wrote in message
news:caahf0rkhyip680xk9kz+3q4uvw79s2dh8denulob_2gxlyf...@mail.gmail.com...
Hi all,
I'm teaching myself perl. Right now, I am stuck with this script. I
don't understand how it works. I know what it does and how to do it by
hand.
$n = 1;
while ($n < 10) {
$sum += $n;
$n += 2;
}
print "The sum is $sum.\n"
I know $sum is initially 0 (undef). I see that $sum becomes 1, then $n
becomes 3. The loop goes back and then I don't understand. Now $sum is
1+3?
Thanks,
JJ
Hello JJ,
It is sometimes helpful to put print statements in a routine to follow the
flow of action. However, if you don't have Perl installed that would be a
problem :-)
$sum += $n;
This statement is shorthand for $sum = $sum + $n;
Whatever value (0 the first time through the loop) is in $sum is added to
the value of $n, (which starts at 1 and increases by 2 for every time though
the loop: $n = $n + 2), and stored in $sum.
In effect, this loop is calculating the sum of odd integers from 1 to 9.
Here it is with some print (say) statements:
#!/usr/bin/perl
use strict;
use warnings;
use 5.014;
my $n = 1;
my $sum;
while ($n < 10) {
say "n: ", $n;
say "sum: ", $sum += $n;
$n += 2;
}
And it prints:
n: 1
sum: 1
n: 3
sum: 4
n: 5
sum: 9
n: 7
sum: 16
n: 9
sum: 25
The loop ends because $n gets incremented to 11 and fails the loop test ($n
< 10).
Hope this helps explain it for you.
Chris
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