How to tell if $query_var isset?

use the indentical comparison operator:

if(get_query_var('cls') !== '' && get_query_var('ch') !== '') {
    mcs_textbook_chapter($dialect, $cls, $ch);
} elseif(get_query_var('cls') !== '') {              
    mcs_textbook_chapter($dialect, $cls);
} else {
    mcs_textbook($dialect);
}

Related Posts:

  1. Using WordPress public query variables
  2. How to Use Wildcards in $wpdb Queries Using $wpdb->get_results & $wpdb->prepare?
  3. MySQL variable in query
  4. Function to delete a post, it’s children and it’s grand children (half way there already)
  5. Nested loop : wich way/order?
  6. Passing parameters to a static front page
  7. Query posts based on previous query
  8. Advanced Custom Fields – Relationship post foreach query
  9. Declaring a var, placing it in a query and using the output of the query?
  10. WordPress is removing query variables like page, p from the URL of a custom static page
  11. Not getting input from get_query_var
  12. WordPress: paginating array using a foreach
  13. “Notice: Undefined variable”, “Notice: Undefined index”, and “Notice: Undefined offset” using PHP
  14. Custom query_var causes displaying posts archive on front page
  15. What is the most efficient way of implementing a favorite post system?
  16. Query by one meta_key and sort by another (possibly NULL value)
  17. Query & Sort Comments by custom comment meta
  18. How to order posts by modified date without using ‘query_posts’?
  19. is_archive() doesn’t work on public query var archive pages?
  20. Specific Loop For 2 Within Each
  21. Inserting data into `post meta` table?
  22. search through post-type attachments titles
  23. cron job to auto delete posts of a specific post type older than x days
  24. How to add a post or page tag to the list of classes appearing in the body tag’s class attribute?
  25. Most effective use of DB querys
  26. Get ID of child from child slug, while knowing parent ID
  27. Two differents queries in archive page
  28. How do I find if a page has a template?
  29. How to set back query var author_name after unset it?
  30. My SQL function to change user_name
  31. How to retrieve elements from another table in a SQL query?
  32. Putting PHP variables into javascript [duplicate]
  33. WordPress Loop: List All Posts by a Category & Subcategory
  34. Why is variable not working on custom sql query using wpdb?
  35. Variable global scope [closed]
  36. Custom filter in admin edit custom post type responding with invalid post type?
  37. Static variable and add_rewrite_rule?
  38. only delete post within query / for each statement (front end)
  39. List all posts from past week grouped by sub-category
  40. Query Custom Post Type posts by Keyword/url slug
  41. how would I create a custom query to get all users, and a related post based on a postmeta field?
  42. Display posts with a start OR end date later than current date
  43. Order posts by custom field DATE value
  44. Pass variable from one function to another
  45. creat filter with wp_query
  46. Increase offset while looping
  47. Form redirect with query vars to page
  48. Query to Get All Users from wp_users With NO matching user_id In wp_usermeta
  49. Two queries for a WP_User_Query search work perfectly apart, but not together
  50. WordPress custom setting page – add flashing message
  51. Custom query AFTER rss fetch_feed not working
  52. Multiple Category Query
  53. list all categories that have a certain word in title
  54. sort query results by newest
  55. How to pass a PHP $_GET variable and fetch/output it?
  56. How to reset usual $query on search page to push custom $wpdb query there?
  57. Order by meta value pro first then meta value free in my search function
  58. How to overwrite orderby with add_query_var
  59. Custom Post not working as expected
  60. persist a variable set in header.php all the way down to footer.php
  61. What is the alternative code to if (isset ($_POST) && !empty ($_POST) to avoid warnings?
  62. How to delete all posts, categories and tags from WordPress database
  63. Ideas how to search & replace post_content when string contains a newline?
  64. Query the WordPress database to get data together with replaced information
  65. How to reference PHP in Javascript
  66. $wpdb->prepare affecting the query?
  67. WordPress SQL search, how to handle SQL Injection?
  68. echo var into wp_query
  69. Query for Custom Post Type UI Does Not Loop All the Post
  70. Querying for specific tags
  71. Limit tags shown in post
  72. Passing PHP Variables to AJAX Loaded Pages
  73. How to manage a particular “order by” for get_search_query()?
  74. Query to view scheduled or draft post
  75. How to add a Variable to post query
  76. Build A Custom SQL Query for WordPress Search
  77. WordPress Custom Form – Getting Query Vars, Weird Glitch?
  78. Reading URL Parameters
  79. How to display variables from plugin?
  80. Trouble migrating custom post types from non-wordpress cms
  81. How to do a MySql query in WordPress?
  82. Pagination in WP Queries
  83. “order” does not affect order of custom query
  84. Create a new post on a specified publish date via link?
  85. Exclude Posts from a Widget
  86. New custom post type entries are not sorted correctly in admin using pre_get_posts
  87. Query String for the WP_QUERY parameters
  88. $wpdb query for price in custom field value
  89. Custom Taxonomy Link Text Echo Name Not Slug
  90. Multiple terms not working on taxonomy
  91. Sorting of coupons in the right way
  92. Unserializeing multiple column values that are stored in one database results variable
  93. excludeCat function reverses order of blog posts
  94. Run search query again without pagination gives no results?
  95. If Elseif Query
  96. How can I add more code to this?
  97. WP_Query orderby meta key/value suddely stopped working
  98. Does wp_query and query_posts affect website performance? [duplicate]
  99. WooCommerce Total # orders [closed]
  100. How to show sticky posts on all pages of the pagination, not just the first page?
techhipbettruvabetnorabahisbahis forumuedusedusedueduedueduseduseduedusedu