CODEWITHSUNDEEP
perl
Andrew
Andrew

Reputation: 6514

Perl - Trouble With Loop Variables

I'm fairly new to coding in Perl and am used to using C-style for loops. I'm not sure why the following program never prints a value of 4 for $l:

use strict;
use warnings;

my $minL = 4;

for (my $l = $minL; $l > 0; $l--) {
    for (my $i = 0; $i + $l < $minL; $i++) {
        print "$i $l\n";
    }
}

Many thanks in advance.

Upvotes: 1

Views: 65

Answers (2)

Ben Grimm
Ben Grimm

Reputation: 4371

In the first iteration:

for (my $l = $minL; $l > 0; $l--) {

$l == $minL 

    for (my $i = 0; $i + $l < $minL; $i++) {

So this block won't run until $l is decremented: 

        print "$i $l\n";
    }

Change your inner loop to: 

    for (my $i = 0; $i + $l <= $minL; $i++) {

Upvotes: 1

hobbs
hobbs

Reputation: 240649

Your inner for loop has the condition $i + $l < $minL. If $l == $minL, then $i + $l < $minL will be false even if $i is 0, so the loop runs 0 times and never prints anything.

Maybe you wanted to use <= for the condition?

By the way, here is how you could write the same thing (assuming the <= condition) using Perl-style foreach loops:

my $minL = 4;
for my $l (reverse 1 .. $minL) {
    for my $i (0 .. $minL - $l) {
        print "$i $l\n";
    }
}

Upvotes: 2

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