my @grades;
@grades[0..39] = ('F') x 50;
@grades[40..49] = ('E') x 50;
@grades[50..59] = ('D') x 50;
@grades[60..64] = ('C') x 50;
@grades[65..69] = ('C+') x 50;
...

##</code><code>##

my @grades;
$_ = 'F' for @grades[0..39];
$_ = 'E' for @grades[40..49];
$_ = 'D' for @grades[50..59];
$_ = 'C' for @grades[60..64];
$_ = 'C+' for @grades[65..69];
...