Perl Temp Converter - perl

Question

Here's my code for Perl, and when I run it, it will display my menu and I can exit with 3. But both 1 and 2 on the menu aren't registering as value input and instead going straight to else and giving an error resulting in an endless loop.
#! c:\Strawberry\perl\bin\Perl.exe
# This is a simple Temperature converter
# that will convert Fahrenheit to Celsius
# and Celsius to Fahrenheit.
use strict;
my $fahr = 0;
my $cel = 0;
my $choice = 0;
my $input = 0;
print "\n";
print "*********************************************\n";
print "*** This is a Temperature Converter ***\n";
print "*********************************************\n";
print "1. Celsius to Fahrenheit.\n";
print "2. Fahrenheit to Celsius. \n";
print "3. Exit\n";
print "*********************************************\n\n";
print "Enter a choice (1-3): ";
my $choice = <STDIN>;
chomp ($choice);
if(&IsNumeric($choice) == 0) {
$choice = 0;
}
while ($choice != 3) {
# Do conversion from C to F
if ($choice == 1) {
print "\nEnter a Temperature: ";
chomp ($cel = "" );
$fahr = ($cel * (9 / 5)) + 32;
# Format to one decimal
$fahr = sprintf("%.1f", $fahr);
print "$cel degrees Celsius = ";
print "$fahr degrees Fahrenheit\n";
}
# Do conversion from F to C
elsif ($choice == 2) {
print "\nEnter a Temperature: ";
chomp ($fahr = "" );
$cel = ($fahr - 32) * 5 / 9;
# Format to one decimal
$cel = sprintf("%.1f", $cel);
print "$fahr degrees Fahrenheit = ";
print "$cel degrees Celsius\n";
}
# Display Error Message
else {
print "\nYou entered and invalid choice please choose a choice from the menu.\n\n";
}
print "\nEnter a Choice (1-3): ";
chomp ($choice = "" );
if(&IsNumeric($choice) == 0) {
$choice = 0;
}
}
# Sub Name: IsNumeric.
# Description: This sub validates the input to check to see if
# the input is a Numeric value
# Example: 100, 1,000, $10.00, and 14.00 are valid inputs.
sub IsNumeric {
my $InputString = shift;
if ($InputString !~ /^[0-9|.|,]*$/) {
return 0;
}
else {
return 1;
}
}

Answer 1

There's a lot of room for improvement in your code, but since this isn't a code review, I'll answer the question you asked and leave it at that. Your pattern of (not) reading input and chomping it is wrong. Instead of this:
print "\nEnter a Temperature: ";
chomp ($cel = "" );
You need to read from STDIN and then chomp without also assigning to an empty string:
$cel = <STDIN>;
chomp($cel);
Or just:
chomp($cel = <STDIN>);
If you had included use warnings at the top of your script, you would have seen the following message or something very similar to it:
Argument "" isn't numeric in numeric ne (!=) at foo.pl line 59,
line 1.
And that would have alerted you that something wasn't being set to the value you thought it was being set to.

Answer 2

Your code never retrieves a temperature. You have
chomp( $cel = "" );
and
chomp ($fahr = "" );
which just assigns the null string to those variables. You need <> in place of ""
Note also that you should never call a Perl subroutine using an ampersand. Wherever you read instructions to do that, it is very out of date. You should also always use warnings 'all' in addition to use strict, and you should avoid using capital letters for local variables
Finally, your regex /^[0-9|.|,]*$/ uses a character class which will match any one of the characters 0 through 9, a comma, a dot or a pipe. I am sure that's not what you meant. Perl won't handle numbers containing comma or pipe characters

Answer 3

After entering an option 1 or 2 you have asked to enter a temperature, but you are not reading this temperature from input.
This chomp ($cel = "" ); and chomp ($fahr = "" );, you didn't read input and choping it. Write it as:
chomp ($cel = <STDIN>);
and
chomp ($fahr = <STDIN>);
And there is no need to declare $choice two times. This code needs lot of improvement.