I've fixed all the problems that I can see but it still throws me the wrong way. Now what ever I enter in the confirm sub activates the else tag of the if statement. And sends me back to confirm()!!! Heres what I've done: (I ran it with warnings on.)

    #To determine the pattern of fish reproducing 
    #in a pond


start();



sub start{

    print "Welcome to the 'Fish in a Pond' chaos theory solution guide
+.\n" . 
                 "Please enter the number of fish in the pond on the f
+irst year:\n";

    print "\n";

    $nof = <STDIN>;

    print "\n";

        print "Please enter the anual rate of increase: \n";

    print "\n";

    $roi = <STDIN>;

    print "\n";

        print "For what period of time would you like the simulation t
+o run for(in years): \n";

        print "\n";
        
        $yrs = <STDIN>;

        chomp($nof);
        chomp($roi);
        chomp($yrs);
        $confirm = confirm();
        
if ($confirm eq 'n')
{
start();
}
elsif($confirm eq 'y')
{
middle();
}
else{
print "Please enter either Y or N. \n";
confirm();
}

}

sub middle{

    $ans = $nof;

        $year = 0;

    print "Year $year.    =    $ans fish.";

    print "\n";

        calc();
}

sub calc{

    while($year <= $yrs) 
{
    $year = $year + 1;
    $i = $ans * $roi;
    $x = 1 - $ans;
    $ans = $i * $x;
        print "Year $year.    =    $ans fish. \n ";
}
}

sub confirm{
print "The data that you have entered says: \n" . 
      "  *  that there is $nof thousand fish in the pond on the fisrt 
+year.\n" .      "  *  that the annual rate of increase is $roi. \n" .
+ 
      "  *  that the simulation will run for $yrs years. \n\n";

print "Is this information correct?(Y/N): ";

$answer = <STDIN>;
$answer =lc($answer);

return($answer);

}
[download]

Help please.
All the Best, Eoin...

If everything seems to be going well, you obviously don't know what the hell is going on.