Use of uninitialized value in concatenation (.) or string at first.pl line 5.

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foreach my $num (@arr) {
        print "Index is: $num. Value is: $arr[$num] ";
}

##</code><code>##

foreach my $num (@arr) {
        print "Index is: $num. Value is: $arr[$num - 1] ";    # Subtract 1 from the index
}

##</code><code>##

for($num = 0; $num<= $#arr;$num++) {

##</code><code>##

for (my $num = 0; ...