Here is a quick snippet to check whether the user is exists or not by user_id in WordPress.

$user = get_userdata( $user_id );
if ( $user === false ) 
{
    // The user doesn't exist
}
else 
{
    // The user exists
}

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Here is a quick snippet to remove woocommerce coupon field from woocommerce checkout page. When you enable the use of coupons, woocommerce adds the apply coupon form in cart and checkout page. For our customization want to remove woocommerce coupon field from checkout page then place the following snippet in functions.php within your theme folder!.

function hide_coupon_field_on_woocommerce_checkout( $enabled ) {
	if ( is_checkout() ) {
		$enabled = false;
	}
	return $enabled;
}
add_filter( 'woocommerce_coupons_enabled', 'hide_coupon_field_on_woocommerce_checkout' );

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Here is a quick snippet to remove woocommerce coupon field from woocommerce cart page. When you enable the use of coupons, woocommerce adds the apply coupon form in cart and checkout page. For our customization want to remove woocommerce coupon field from cart page then place the following snippet in functions.php within your theme folder!.

function hide_coupon_field_on_woocommerce_cart( $enabled ) {
	if ( is_cart() ) {
		$enabled = false;
	}
	return $enabled;
}
add_filter( 'woocommerce_coupons_enabled', 'hide_coupon_field_on_woocommerce_cart' );

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Here is a quick snippet to add new custom currency and symbol to wocommerce. Place the following snippet in functions.php within your theme folder. After adding this code your currency will be available in your WooCommerce settings page.

add_filter( 'woocommerce_currencies', 'add_my_custom_currency' );

function add_my_custom_currency( $currencies ) {
     $currencies['BOO'] = __( 'Your currency name', 'woocommerce' );
     return $currencies;
}

add_filter('woocommerce_currency_symbol', 'add_my_custom_currency_symbol', 10, 2);

function add_my_custom_currency_symbol( $currency_symbol, $currency ) {
     switch( $currency ) {
          case 'BOO': $currency_symbol = '$'; break;
     }
     return $currency_symbol;
}

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Add the following code in functions.php within your theme folder for redirect customers into home page after logout in WordPress

add_filter('logout_url', 'new_logout_url', 10, 2);
function new_logout_url($logouturl, $redir)
{
	$redir = get_option('siteurl');
	return $logouturl . '&redirect_to=' . urlencode($redir);
}

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You can use the following code for add custom CSS in WordPress. add your styles in commented part.

add_action(‘admin_head’, ‘my_study_style’);
function my_study_style()
{
//add your styles here
}

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You can use the function get_the_category_list() for this process.

<?php
$categories = get_the_category();
$separator = ' ';
$output = '';
if($categories){
	foreach($categories as $category) {
		$output .= '<a href="'.get_category_link( $category->term_id ).'" title="' . esc_attr( sprintf( __( "View all posts in %s" ), $category->name ) ) . '">'.$category->cat_name.'</a>'.$separator;
	}
echo trim($output, $separator);
}
?>

For more : http://codex.wordpress.org/Template_Tags/get_the_category

Uploaded images are stored as posts with the type “attachment”. Use get_posts() and query for all attachments:

$args = array(
                'post_type' => 'attachment',
                'numberposts' => -1,
                'post_mime_type' =>'image',
                'post_status' => 'inherit',
                'post_parent' => null, // any parent
           );
$attachments = get_posts($args);
if ($attachments) {
    foreach ($attachments as $post) {
         setup_postdata($post);
         the_title();
         the_attachment_link($post->ID, false);
         the_excerpt();
     }
}

Now All images are displayed.

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<input type="text" id="city" name="city" autocomplete="off"/> 
<div id="key"></div>

     var ajaxurl="<?php echo admin_url( 'admin-ajax.php' ); ?>"; 
     var data ={ action: "city_action",  city:cid    };
        $.post(ajaxurl, data, function (response){
                     $('#key').html(response);
           });

       function city_action_callback() {     
       global $wpdb;
            $city=$_GET['city'];
            $result =   $mytables=$wpdb->get_results("select * from ".$wpdb->prefix . "mycity where city like '%".$city."'" );   
            $data = "";
            echo '<ul>'
            foreach($result as $dis)
            {
                         echo '<li>'.$dis->city.'</li>';
            }
            echo '</ul>'    
         die();
       }

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If you want to get category id by using category name then use the following code

function get_category_id($cat_name){
	$term = get_term_by('name', $cat_name, 'category');
	return $term->term_id;
}

then Just call the function with your category name as a parameter. for example

$category_ID = get_category_id('Books');

Now you can get the category Id in variable $category_ID.

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