# do this once:
my @grades = (
     ('F' ) x 40,   #  0..39
     ('E' ) x 10,   # 40..49
     ('D' ) x 10,   # 50..59
     ('C' ) x  5,   # 60..64
     ('C+') x  5,   # 65..69
     ...
);

# do this many times:
my $grade = $grades[$ARGV[0]];
print "The student has gotten a $grade grade for the score of $ARGV[0].";