Stacks are a data structure that allows items to be pushed and popped off the top of the stack. This makes them perfect for implementing queues and last in, first out (LIFO) data structures.
The basic stack consists of a list of items, with a pointer to the first item and a pointer to the last item. The last item in the stack is also known as the top of the stack.
To push an item onto the stack, we simply update the pointer to the first item to point to the new item. To pop an item off the stack, we simply update the pointer to the last item to point to the previous item.
How to use stacks?
Stacks are generally used to store items that are going to be used later. For example, a stack can be used to store the characters that are being typed into a text editor. The editor can push each character onto the stack as it is typed and then pop them off when they are needed. This ensures that the characters are processed in last in, first out order.
Doing this allows the text editor to see what will be displayed before it runs any code that changes what is displayed. For example, if the user types ‘hello’, then presses backspace to delete the last letter, ‘o’ , then types ‘goodbye’, there are three items on the stack – ‘h’, ‘e’, and ‘l’.
Why use stacks?
Stacks are very efficient at removing items from the top of a stack. This makes them ideal for implementing queues, where items need to be removed in first in, first out order.
What are stacks used for?
Stacks are used in vast numbers of systems and everyday programs. A few examples include:
- Menu systems, where each item in the menu will be popped off the stack when it is selected.
- Compilers and assemblers, which use stacks to store information about different variables and symbols.
- Text Editors, which “push” characters onto a stack as they are typed. The text editor can then pop the characters back off the stack when they are needed to display the text on screen.
- Operating Systems, which use stacks to store information about running processes and threads.
- Networks, where packets of data are “pushed” onto a queue for transmission over the network.
- A web browser will push each HTML element onto a stack as it is parsed. This stack is then used to determine the order in which the elements should be displayed on the screen.
Stacks are a data structure that allows items to be pushed and popped off the top of the stack. This makes them perfect for implementing queues and last in, first out (LIFO) data structures.
How to create a stack?
A stack is generally implemented as a linked list with a pointer to the first item and a pointer to the last item. When an item is pushed onto the stack, we change the value of the first and last pointers so that they point at the new top of the stack. When an item is popped off, we just reverse this process.
What does a stack look like?
The diagram below shows the contents of a stack after six values have been pushed onto it. The last pointer is shown in red and the first pointer is shown in green. Notice how they both point at the same value, as we are looking at the top of the stack.
Conclusion
Stacks are generally used to store items that are going to be processed later. For example, a stack can be used to store the characters that are being typed into a text editor. The editor can push each character onto the stack as it is typed and then pop them off when they are needed. This ensures that the characters are processed in last in, first out order.