#!/usr/bin/perl -w

use strict;

my %grades;

while (<DATA>) {
     chomp;
     my($student,$grade) = split (" ",$_);
     $grades{$student} .= $grade . " ";
     #$grades{$student} = $grade;
     print "\$grades{$student} is $grades{$student}\n";
      
}

for (sort keys %grades) {
    my $scores = 0;
    my $total  = 0; 
    my @grades = split(" ", $grades{$_});
    for (@grades) {
       $total += $_;
       $scores++;
    }
    my $average = $total / $scores;
    print "$_: $grades{$_}\tAverage: $average\n";
}

__END__
lee  90
lee  100
kim  90
kim  90




./././perl.score
$grades{lee} is 90 
$grades{lee} is 90 100 
$grades{kim} is 90 
$grades{kim} is 90 90 
kim: 90 90      Average: 90
lee: 90 100     Average: 95


so 
$grades{$student} .= $grade . " "; is more like

$grades
[download]

#!/usr/bin/perl -w

use strict;
use diagnostics;

my %grades;
my %student_n;

while (<DATA>) {
     chomp;
     my($student,$grade) = split (" ",$_);
     $grades{$student} += $grade;
     $student_n{$student}++;
}

for (sort keys %grades) {
    my $avg = $grades{$_} / $student_n{$_};
    print "$_ average of $student_n{$_} exams are $avg\n";
}

__END__
lee  90
lee  100
kim  90
kim  90
~

./././././perl.score_copy
kim average of 2 exams are 90
lee average of 2 exams are 95
[download]

so
$grades{$student} .= $grade . " "; is more like

$grades

No. It is this:


$grades{$student} = "$grades{$student}$grade ";
[download]


The value of $grade, followed by a space (" "), is appended to any existing value of $grades{$student}. The . operator does texual concatination, whereas += is numeric, and will add the right-hand-side to the left. For example:


$x = 3;
$y = 4;
$x .= $y;  # gives 34
$x += $y;  # gives 7
[download]

No. It's more like

$grades{$student} = $grades{$student} . $grade . " ";
[download]