Dear Wise and Serene Monks,

I have made a code that gives the expected result but gives a lot of warnings, so it means my code shoud be cleaner
Could you tell me how ?

Here is the start file : 
08:48:45;"";"";;"";
08:49:43;"DAL11";"08:47";527;"08:50";530
08:50:41;"";"";;"";
08:51:40;"";"";;"";
08:52:38;"";"";;"";
08:53:36;"ACA879";"08:51";531;"08:53";533
08:54:35;"";"";;"";
08:55:33;"SHT8K";"08:48";528;"08:55";535
08:56:31;"";"";;"";
08:57:30;"DLH9FM";"08:53";533;"08:57";537

[download]

Here is my code : 
#!/usr/bin/perl
use strict;
use warnings;
use diagnostics;


#################  IN WHICH DIRECTORY WE ARE ########################

my $Current_Dir = `pwd`;
print STDOUT "the current directory is $Current_Dir";

#####################################################################

################### OPEN THE FIRST INFILE ############################
# open the first file 
# do not forget the "" to declare  my ${first_file} = 

my ${first_file} = "$ARGV[0]";
open(INFILE,"<${first_file}") or die "Can't open ${first_file} : $!";

#################################################################


################### OPEN THE OUTFILE ############################
# name of the OUTFILE
# never put a \n at the end of the OUTFILE name otherwise it does not 
+create the output
 my ${outfile_name} = "Analysis_${first_file}";

# to open the file
# OUTFILE is the name of the HANDLE in this case
  open (OUTFILE, ">${outfile_name}") or die "Can't open ${outfile_name
+}: $!";

##################################################################

    while (<INFILE>){


    chomp($_);
    my @Parts = split(";");
    my $aircraft_id = $Parts[1];
    my $ATO_min = $Parts[3];
    my $CTO_min = $Parts[5];
    my $ATO = $Parts[2];
    my $CTO = $Parts[4];

    my $delay_ATO_CTO_min;

    if (($CTO =~ /(\d\d):(\d\d)/) & ($ATO =~ /(\d\d):(\d\d)/)){
        $delay_ATO_CTO_min = $CTO_min-$ATO_min;
        }
        else{
        $delay_ATO_CTO_min = "";
        }



    my $flight_big_delay;

        # condition on the delay
        if ($delay_ATO_CTO_min > 10){
        $flight_big_delay = $aircraft_id;
        print OUTFILE "$aircraft_id;$ATO_min;$CTO_min;$delay_ATO_CTO_m
+in;$flight_big_delay\n";
        }
        else{
        print OUTFILE "$aircraft_id;$ATO_min;$CTO_min;$delay_ATO_CTO_m
+in\n";
        }
    
    }
close INFILE;
close OUTFILE;

[download]

Here is my output file 
"";;;
"DAL11";527;530;3
"";;;
"";;;
"";;;
"ACA879";531;533;2
"";;;
"SHT8K";528;535;7
"";;;
"DLH9FM";533;537;4

[download]

And here are the warnings: 
Argument "" isn't numeric in numeric gt(>) at Monks_Treatment.pl (that
+'s the name of the program) line 60, <INFILE>

[download]
update : the update concerns both the input and output since the original post data copied from wordpad, not from excel, for the input data as well as the output data

In reply to warnings unexpecetd by steph_bow

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
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