PHP Function returns wrong date - php

Question

I' am learning how to make a WordPress Plugin. I did make few simple plugins but not as complicated as this one. It's a Events Calendar. The var_dump from the function "nc_get_start_date()" on the page it outputs wrong dates.
The output from the var_dump(nc_get_start_date());
string(32) "1970-01-01,1970-01-01,1970-01-01"
This is what the function should return in real
23-12-2013, 25-12-2013, 26-12-2013
In the function.php on the plugin folder. This is the codes
/* Query to get the events post from the database */
function get_nc_events(){
global $post;
$query = new WP_Query(
array(
'post_type' => 'events',
'post_status' => 'publish',
'posts_per_page' => -1,
'order' => 'ASC'
)
);
return $query;
}
/* Get the start date from the above function */
function nc_get_start_date(){
$query = get_nc_events();
while ( $query->have_posts() ) : $query->the_post();
$nc_event_id = $post->ID;
$wnc_start_date = get_post_meta( $nc_event_id, 'wnc_start_date');
$wnc_start_date = $wnc_start_date[0];
$wnc_start_date = date("Y-m-d", strtotime($wnc_start_date));
$wnc_start_date_array .= "$wnc_start_date,";
endwhile;
return rtrim($wnc_start_date_array, ",");
}
When I write the code in page-caledar.php without the function it renders everything prefectly.
$query = get_nc_events();
while ( $query->have_posts() ) : $query->the_post();
$nc_event_id = $post->ID;
$wnc_start_date = get_post_meta( $nc_event_id, 'wnc_start_date');
echo $wnc_start_date = $wnc_start_date[0] . "<br/>";
endwhile;

Answer 1

Problem Solved. Thanks everyone. The problem was in this function
/* Get the start date from the above function */
function nc_get_start_date(){
global $post;
$query = get_nc_events();
while ( $query->have_posts() ) : $query->the_post();
$nc_event_id = $post->ID;
$wnc_start_date = get_post_meta( $nc_event_id, 'wnc_start_date');
$wnc_start_date = $wnc_start_date[0];
$wnc_start_date = date("Y-m-d", strtotime($wnc_start_date));
$wnc_start_date_array .= "$wnc_start_date,";
endwhile;
return rtrim($wnc_start_date_array, ",");
}
I didn't make global $post;