How to check whether a posted value exists?

if ( $template->get_posted_value( 'dob_month' ) )

Thank you very much and finally how can I then compare that value?

For example:

$myMonth = "February";

if ( $template->get_posted_value( 'dob_month' )  && **posted value is equal to $myMonth**) {

echo "The submitted month matches the variable!";

}

if ( $template->get_posted_value( 'dob_month' ) == '12' ) {
    echo 'You were born in December!';
}

https://php.net/manual/en/language.operators.comparison.php