What happens if $acc_bal is exactly 1.0? You are doing a chomp on $bak_id, so it can never be "\n" (unless you changed $/). In might also be a good idea to chomp $acc_bal, if only for consistency.

I was trying to use Switch fuction but its not working in PERL V 5.8.4

Yes, pity Switch was put into the base. The switch/case statement has had a chequered history. There is a new one in 5.10, but for now:

#!/usr/bin/perl 
use strict;
use warnings;  

my $bak_id;
my $acc_bal;

chomp($bak_id =<STDIN>);
chomp($acc_bal=<STDIN>);

SWITCH: {
    (!$bak_id or !$acc_bal) && do {
        print "Returning to Main Menu\n";
        return;    # or somesuch
    };
    
    ($acc_bal < 1.0 && $bak_id eq "BOTH") && do {
        print "condition 1\n";
        last SWITCH         
    };
    
    ($acc_bal > 1.0 && $bak_id eq "BOTH") && do {
        print "condition 2\n";
        last SWITCH
    };

    ($acc_bal < 1.0 && $bak_id =~ /^Cust[12]$/) && do {
        print "condition 3\n";
        last SWITCH
    };

    ($acc_bal > 1.0  && $bak_id =~ /^Cust[12]$/) && do {
        print "condition 4\n";
        # blah, blah, blah
        last SWITCH
    };

    print "Invalid entry\n";

}
[download]