Wordpress functions

Retrieve template directory URI for the current them
 <?php echo get_template_directory_uri(); ?>  

Retrieves the absolute path to the directory of the current there

echo get_template_directory();

Is home or front page
if( is_home() || is_front_page() ) { }


User functions:

update user info

update_user_meta$user_id$meta_key$meta_value$prev_value ); update_user_meta

Get post by ID

get_post$id$output$filter ); for detail

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Wordpress images function

get featured image
 
if (has_post_thumbnail( $post->ID ) ){
   echo wp_get_attachment_image( get_post_thumbnail_id(), 'full');
}