perl: switch statements

#!/usr/local/bin/perl -c
                               ^ here?

perldoc -q switch

perldoc Switch

use Switch;

chomp( my $score = <STDIN> );

switch( $score ) {
    case [90..100] { print "\n\nYou have an A!\n\n;" }
    case [80..89] { print "\n\nYou have an B!\n\n;" }
    case [70..79] { print "\n\nYou have an C!\n\n;" }
    case [60..69] { print "\n\nYou have an D!\n\n;" }
    case [0..59] { print "\n\nYou have an F!\n\n;" }

    else { print "\n\nError: scores may not be less than 0 or greater than 100.\n\n"; }
}

-c just compile, dont run

#!/usr/local/bin/perl
use Switch;
chomp( my $score = <STDIN> );

switch( $score )
{
    case [90..100] { print "\n\nYou have an A!\n\n;" }
    case [80..89] { print "\n\nYou have an B!\n\n;" }
    case [70..79] { print "\n\nYou have an C!\n\n;" }
    case [60..69] { print "\n\nYou have an D!\n\n;" }
    case [0..59] { print "\n\nYou have an F!\n\n;" }

    else { print "\n\nError: scores may not be less than 0 or greater than 100.\n\n"; }
}

I tried use Switch;
but it couldn't locate it: Can't locate Switch.pm in @INC

do perl -h and you will find:

 -c              check syntax only (runs BEGIN and CHECK blocks)

what is the output of

 perl -v

Is it because the unix system I'm using doesn't have it?

maybe you have a old version

This is perl, version 5.005_03 built for sun4-solaris

Copyright 1987-1999, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5.0 source kit.

Complete documentation for Perl, including FAQ lists, should be found on
this system using `man perl' or `perldoc perl'.  If you have access to the
Internet, point your browser at http://www.perl.com/, the Perl Home Page.

You need a newer version of perl
actually I have version 5.8.7 and you have 5.5.3. Switch module just apperard on the version 5.8.x

I would say that 90% of the Perl programmers never used that module

Darn.  Well, would i have to do it the old if/else way then if I can't use switch?

perldoc -q switch

Your switch statement might not have done what you wanted anyway for $score=90.1

I would do

sub in {
    my $elem = shift;
    foreach my $value (@_) {
        return 1 if $value eq $elem;
    }
    return 0;
}

chomp( my $score = <STDIN> );

if (in($score=>(90..100))) {
    print "\n\nYou have an A!\n\n;"
} elsif (in($score=>(80..89))) {
    print "\n\nYou have an B!\n\n;"
} elsif (in($score=>(70..79))) {
    print "\n\nYou have an C!\n\n;"
} elsif (in($score=>(60..69))) {
    print "\n\nYou have an D!\n\n;"
} elsif (in($score=>(0..59))) {
    print "\n\nYou have an E!\n\n;"
} else {
    print "\n\nError: scores may not be less than 0 or greater than 100.\n\n";
}
   

perl grades.pl 50.2



You have an A!

Uh, oh!  That's not right...


chomp( my $score = <STDIN> );

for ($score) {
    if    (90 >= $score && $score <= 100)  { print "\n\nYou have an A!\n\n"; }
    elsif (80 >= $score && $score <= 89)  { print "\n\nYou have an B!\n\n"; }
    elsif (70 >= $score && $score <= 79)  { print "\n\nYou have an C!\n\n"; }
    elsif (60 >= $score && $score <= 69)  { print "\n\nYou have an D!\n\n"; }
    elsif (0 >= $score && $score <= 59)  { print "\n\nYou have an F!\n\n"; }
    else  { print "\n\nError: scores may not be less than 0 or greater than 100.\n\n"; }
}

my %in;
@in{0..100}=(("E")x60,("D")x10,("C")x10,("B")x10,("A")x11);

chomp( my $score = <STDIN> );
if( my $grade = $in{$score} ){
  print "\n\nYou have an $grade!\n\n;"
}else{
  print "\n\nError: scores may not be less than 0 or greater than 100.\n\n";
}

oh, that's how you do the range

   if    (90 <= $score && $score <= 100)  { print "\n\nYou have an A!\n\n"; }
    elsif (80 <= $score && $score < 90)  { print "\n\nYou have an B!\n\n"; }
    elsif (70 <= $score && $score < 80)  { print "\n\nYou have an C!\n\n"; }
    elsif (60 <= $score && $score < 70)  { print "\n\nYou have an D!\n\n"; }
    elsif (0 <= $score && $score < 60)  { print "\n\nYou have an F!\n\n"; }
    else  { print "\n\nError: scores may not be less than 0 or greater than 100.\n\n"; }

if( my $grade = $in{int $score} ){

perl grades.pl 50.2  #this looks like you want to get $score from @ARGV


chomp( my $score = <STDIN> ); #but this is reading $score from <STDIN>

oh... so I can't use <STDIN> to read input from prompt?

for reading parameters, you have the @ARGV

For reading for stdin you have <STDIN>

for reading from a files in @ARGV or from stdin you have <>

if( my $grade = $in{int $score} ){ # but this would allow $score = 100.9 or $score = -0.5, contrary to the requirements stated in the Error message

Ah, $score = $ARGV[0]; fixed it.

chomp( my $score = <STDIN> );
$score = $ARGV[0];

for ($score) {
    if    (90 <= $score and $score <= 100)  { print "\n\nYou have an A!\n\n"; }
    elsif (80 <= $score and $score < 90)  { print "\n\nYou have an B!\n\n"; }
    elsif (70 <= $score and $score < 80)  { print "\n\nYou have an C!\n\n"; }
    elsif (60 <= $score and $score < 70)  { print "\n\nYou have an D!\n\n"; }
    elsif (0  <= $score and $score < 60)  { print "\n\nYou have an F!\n\n"; }
    else  { print "\n\nError: scores may not be less than 0 or greater than 100.\n\n"; }
}


Does this look good?

It seems to catch all the errors.

my $score = $ARGV[0];

for ($score) {
    if    (90 <= $score and $score <= 100)  { print "\n\nYou have an A!\n\n"; }
    elsif (80 <= $score and $score < 90)  { print "\n\nYou have an B!\n\n"; }
    elsif (70 <= $score and $score < 80)  { print "\n\nYou have an C!\n\n"; }
    elsif (60 <= $score and $score < 70)  { print "\n\nYou have an D!\n\n"; }
    elsif (0  <= $score and $score < 60)  { print "\n\nYou have an F!\n\n"; }
    else  { print "\n\nError: scores may not be less than 0 or greater than 100.\n\n"; }
}

if you're going to do
$score = $ARGV[0];
then
chomp( my $score = <STDIN> );
seems pointless

do you need the STDIN?

chomp( my $score = <STDIN> );

What happens if I comment out the for loop?  Will this still perform what it's supposed to do?

what?

> chomp( my $score = <STDIN> );
> seems pointless


Oops!  That was supposed to be commented out.

> what?

Just use the if/else, no need for loop.

you are correct

    my $score = $ARGV[0];

    if    (90 <= $score and $score <= 100)  { print "\n\nYou have an A!\n\n"; }
    elsif (80 <= $score and $score < 90)  { print "\n\nYou have an B!\n\n"; }
    elsif (70 <= $score and $score < 80)  { print "\n\nYou have an C!\n\n"; }
    elsif (60 <= $score and $score < 70)  { print "\n\nYou have an D!\n\n"; }
    elsif (0  <= $score and $score < 60)  { print "\n\nYou have an F!\n\n"; }
    else  { print "\n\nError: scores may not be less than 0 or greater than 100.\n\n"; }

If you're going to use
for ($score) {
then you can say

for( $score ){
    if    (90 <= $_ && $_ <= 100)  { print "\n\nYou have an A!\n\n"; }
    elsif (80 <= $_ && $_ < 90)  { print "\n\nYou have an B!\n\n"; }
    elsif (70 <= $_ && $_ < 80)  { print "\n\nYou have an C!\n\n"; }
    elsif (60 <= $_ && $_ < 70)  { print "\n\nYou have an D!\n\n"; }
    elsif (0  <= $_ && $_ < 60)  { print "\n\nYou have an F!\n\n"; }
    else  { print "\n\nError: scores may not be less than 0 or greater than 100.\n\n"; }
}

Seems to work okay.  The program is supposed to end after it matches one grade.

Yeah, I think I'll take out the for loop.

Or


    my $score = $ARGV[0];
    if    (90 <= $score and $score <= 100)  { print "\n\nYou have an A!\n\n"; }
    elsif (80 <= $score)  { print "\n\nYou have an B!\n\n"; }
    elsif (70 <= $score)  { print "\n\nYou have an C!\n\n"; }
    elsif (60 <= $score)  { print "\n\nYou have an D!\n\n"; }
    elsif (0  <= $score)  { print "\n\nYou have an F!\n\n"; }
    else  { print "\n\nError: scores may not be less than 0 or greater than 100.\n\n"; }

Okay, thank you!  Points time.

my $score = $ARGV[0];  --> would I have to use strict;  ?

my $score = $ARGV[0];
    if    (90 <= $score and $score <= 100)  { print "\n\nYou have an A!\n\n"; }
    elsif (80 <= $score)  { print "\n\nYou have an B!\n\n"; } #this will give a B grade for $score=110

no, but you should.

Forces you to declare the variables, avoiding many errors

Basically is a good practice

   my $score = $ARGV[0];
    if (100 < $score )   { print "\n\nError: scores may not be greater than 100.\n\n"; }
    elsif (90 <= $score)  { print "\n\nYou have an A!\n\n"; }
    elsif (80 <= $score)  { print "\n\nYou have an B!\n\n"; }
    elsif (70 <= $score)  { print "\n\nYou have an C!\n\n"; }
    elsif (60 <= $score)  { print "\n\nYou have an D!\n\n"; }
    elsif (0  <= $score)  { print "\n\nYou have an F!\n\n"; }
    else  { print "\n\nError: scores may not be less than 0.\n\n"; }

use warnings; #can also be helpful

warnings shall not be avaible, but you have them as
perl -w

So basically, all my programs should have the use strict and use warnings?  Just to be on the safe side?

basically yes.

in older versions you dont have warnings, but 'perl -w' is similar

or
$^W=1;
There are legitimate reasons for turning off strict and/or warnings, but until you know what they are, they can help you discover problems yourself without having to wait for someone to answer here