A subroutine with a series of returns is one way to make the logic simple and clear: 

#!/usr/bin/env perl
use Modern::Perl;

sub figure_grade {
    my $n = shift;
    return undef if $n =~ /\D/ or $n > 100 or $n < 0;
    return 'A'   if $n > 79; # 80% == A?  Serious grade inflation!
    return 'B+'  if $n > 74;
    return 'B'   if $n > 69;
    return 'C+'  if $n > 64;
    return 'C'   if $n > 59;
    return 'D'   if $n > 49;
    return 'E'   if $n > 39;
    return 'F';
}

my $g = figure_grade($ARGV[0]);
if($g){
    say "The student has gotten the grade $g for the score of $ARGV[0]
+";
} else {
    say "Please enter a value between 0 and 100";
}

[download]

Aaron B.
My Woefully Neglected Blog, where I occasionally mention Perl.

In reply to Re: conditional statement by aaron_baugher
in thread conditional statement by victorlai

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.