use strict;
use warnings;

my ( $i, $j, $x, $tot );
my @exes;

print "Please enter for how many values of x you will be finding the Standard Deviation.\n";

do {
    chomp( $i = <> );
    print "\nPlease only use numbers.\n" if $i =~ m/\[1-9]/;
} until ( $i !~ m/\[1-9]/ );

print "\nPlease input the values of x, one at a time.\n";

for $j ( 1 .. $i ) {
    do {
        chomp( $x = <> );
        print "\nPlease only use numbers.\n" if $x =~ m/\[1-9]/;
    } until ( $x !~ m/\[1-9]/ );

    push @exes, $x;
}

undef $x;

for (@exes) {
    $x = $x + $_;
}

my $ave = $x / $i;

for (@exes) {
    $tot = $tot + ( ( $_ - $ave ) ^ 2 );
}

my $deviation = sqrt( $tot / $n );

print "\nThe Standard Deviation of that set of numbers is $deviation.\n";