Queue Data Structure & Operations (Linked List Based) | C Programming Example

How to implement a queue data structure in C using a linked list as the underlying data structure, including a library of functions that implement the operations enqueue, dequeue, peek, size and is empty.
Source code: github.com/portfoliocourses/c....
See the Wikipedia article on Queue data structures: en.wikipedia.org/wiki/Queue_(....
Also see these videos on concepts used in this video...
Introduction To Pointers: • Introduction to Pointe...
Dynamic Memory Allocation: • Dynamic Memory Allocat...
Struct Basics: • struct Basics | C Prog...
Typedef Basics: • typedef Basics | C Pro...
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[@lawniczakjohn]

Oooh baby! DS&A time. Anyone discovering this channel for the first time, it’s a great resource.

[@PortfolioCourses]

Thanks John! :-) Lately I've wanted to make more DS&A videos, I'm thinking of doing some in C++ next...

[@dimitrioskalfakis]

well thought-out narrative with a comprehensive and clear presentation.

[@PortfolioCourses]

That's excellent to hear you found it to be comprehensive and clear, thank you for the kind feedback! :-)

[@martinnyagah4313]

I appreciate the effort you put to teach us! Thank you sir!

[@PortfolioCourses]

You're very welcome Martin! :-)

[@Neberdine]

You are the best. Thanks for all the help you provide.

[@PortfolioCourses]

You're welcome, and thank for the kind words! :-)

[@fbi873]

This is an amazing video. Thanks for your efforts.

[@PortfolioCourses]

I'm glad you enjoyed, and you're welcome! :-)

[@yigitcoban9823]

I appreciate the coding sources, If ı miss something which is important, ı can get it from the source code's subtitle. Thank you Mr. Kevin.

[@PortfolioCourses]

You're welcome! :-)

[@Matheusk0]

Hey, I love your tutorials, thanks a lot for you work, pointers and data structures haven been a bit difficult for me to learn but your explanations always help me understand them with ease. I have a question: At the beginnning when you were defining the Node struct, you defined " typedef struct Node " and then typed "Node" again after the closing curly bracket. Why was the first "Node" needed? Since right after at the Queue struct definition you only set "Queue" once, after the closing curly bracket. Also, inside the Node struct definition, you used " struct Node *next; " to define the pointer to the next value in the list, and I was wondering if the "struct" word was needed for that, since you already had defined an alias for that struct. Couldn't that line have been just " Node *next; "? Or can we not use aliases when working with pointers? Thanks a lot again!

[@saad-jad]

Inside the while loop in the destroy_queue function, you created a temp variable which I think is unnecessary, because currentNode is enough to traverse. Consider this code and correct me if I'm wrong. while (currentNode !=NULL){ currentNode=currentNode->next; free(queue->head); queue->head=currentNode; } // end of while I know the difference may not be noticeable, but I think less variables are better. Love your vids! Have a blessed day.

[@PortfolioCourses]

No currentNode is not enough to traverse the list while also free-ing the current node. Here you're using queue->head in a bit of a similar way to the "temp variable", which is OK too. :-)

[@wuvorwenda6733]

I learned a lot thank you.

[@PortfolioCourses]

I'm glad you learned a lot, and you're welcome! :-)

[@beholdenspore28]

returning null from qequeue() causes a warning with clang (idk about gcc). to fix it, just return 0 instead.

[@Brad_Script]

that's because it's supposed to return an int not a pointer, although the returned value could be anything because the operation failed.

[@theayushagrawal2550]

Can you please create a video on implementation of queue using array (or stack)

[@anoshiravan6809]

thank you

[@laputa4825]

Hello I have a question, I want to access structure variables but I have to do it through functions with a "custom" ADT. GET functions will return the requested variable, while SET functions will require the variable being changed and the new value as parameters. While there is a condition that direct access to the structure variables is not allowed outside of the ADT implementation. How would I approach this? I am very lost. Is there any videos that can help with understanding this?

[@PortfolioCourses]

The only approach I know of to "hiding access to the structure members" is to have functions as part of a library which provide and work with void pointers, while using a struct internally. e.g. what is discussed here: stackoverflow.com/a/2672067. Unfortunately I'm unaware of a good resource to learn about how to do that, and I don't have a video on that.

[@anime--A]

which compiler iis that

[@ivanraulsanchezdiaz7499]

What happens if I don't use malloc to create the queue?

[@ivanraulsanchezdiaz7499]

Queue create_queue() { Queue queue; queue.head = NULL; queue.tail = NULL; queue.size = 0; return queue; } the queue only needs the space of two pointers and the integer that indicates the size, right?

[@PortfolioCourses]

Good question Ivan! :-) If you don’t use malloc then the Queue will be in a place in memory called the stack rather than the heap. When you pass the Queue around or return it the Queue is being copied each time essentially, with malloc there is one copy of the Queue struct on the heap, and we just pass around and copy a pointer value to it. Either way works really!

[@ivanraulsanchezdiaz7499]

@@PortfolioCourses ohh i see, in some cases it's cheaper just to return the pointer, thanks a lot for you reply!

[@jjfan4014]

In enqueue, queue->tail->next = newNode; this should be wrong because tail points to NULL at that time. It should be a segmentation fault.

[@PortfolioCourses]

We check if the queue is empty before accessing the tail. If the queue is not empty, there is a tail, and we can access next. And if the queue is empty and we create a new node, then note how both head and tail point to that same node. if (is_empty(queue)) { queue->head = newNode; queue->tail = newNode; } else { queue->tail->next = newNode; queue->tail = newNode; }

[@jjfan4014]

Thank you@@PortfolioCourses

[@PortfolioCourses]

@@jjfan4014 You're welcome! 🙂

[@PortfolioCourses]

If you liked this video you might like learning more about Linked Lists! :-) I've made this "lowest possible price" coupon course for the Udemy Linked List course that expires on March 26th 11:50pm PST: www.udemy.com/course/linked-lists-with-c/?couponCode=5DAYDISCOUNT.

[@thesmug2750]

Why do you talk like that? “Kudidastructure” 🤣