Programming Perl, 4th Edition

An Average Example

Suppose you’ve been teaching a Perl class, and you’re trying to figure out how to grade your students. You have a set of exam scores for each member of a class, in random order. You’d like a combined list of all the grades for each student, plus their average score. You have a text file (imaginatively named grades) that looks like this:

Noël 25
Ben 76
Clementine 49
Norm 66
Chris 92
Doug 42
Carol 25
Ben 12
Clementine 0
Norm 66
...

You can use the following script to gather all their scores together, determine each student’s average, and print them all out in alphabetical order. This program assumes rather naïvely that you don’t have two Carols in your class. That is, if there is a second entry for Carol, the program will assume it’s just another score for the first Carol (not to be confused with the first Noël).

By the way, the line numbers are not part of the program, any other resemblances to BASIC notwithstanding.

 1 #!/usr/bin/perl 2 use v5.14; 3 4 open(GRADES, "<:utf8", "grades") || die "Can't open grades: $!\n"; 5 binmode(STDOUT, ':utf8'); 6 7 my %grades; 8 while (my $line = <GRADES>) { 9 my ($student, $grade) = split(" ", $line); 10 $grades{$student} .= $grade . " "; 11 } 12 13 for my $student (sort keys %grades) { 14 my $scores = 0; 15 my $total = 0; 16 my @grades = split(" ", $grades{$student}); 17 for my $grade (@grades) { 18 $total += $grade; 19 $scores++; 20 } 21 my $average = $total / $scores; 22 print "$student: $grades{$student}\tAverage: $average\n"; ...