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Implementing a Stack in C

Hello, dear friends! My name is Sergey Balakirev and in this lesson, we will implement a small program to create a stack data structure using the knowledge we acquired earlier.

What is a Stack?

A stack is a data structure that adds new objects to the top and extracts from the top as well. This creates a queue in which the last added object is extracted first. In English, this is abbreviated as LIFO (Last in, first out).

Implementing the Stack

In our program, we will implement the stack as follows:

  • Each element/object in the stack will have a Delta field to store the data.
  • The Next pointer is a pointer to the next element in the stack. If it corresponds to the last object in the stack, the value of Next will be null.
  • Additionally, the stack will have a Top pointer that always points to the topmost object.

To do this, we will first declare this structure using the keyword typedef. We will introduce a new data type that represents this structure. The Next pointer has the type struct Tag object, which is the same type we are currently defining.

It is a so-called "incomplete" data type, as we have not fully declared it yet. However, this is enough information for the compiler to make a pointer of this type.


Using Pointers in a Stack Data Structure

When implementing a stack data structure, using pointers can be a useful technique for creating an intuitive and efficient implementation. In particular, using a pointer to keep track of the top element of the stack can simplify the implementation. However, there are some nuances to using pointers in a stack that should be kept in mind in order to avoid errors.

Here, we will outline a basic implementation of a stack using pointers and explain some of the important details to keep in mind.

Declaring a Pointer to the Top of the Stack

The first step when implementing a stack using a pointer is to declare the pointer to the top of the stack. Within the structure of the stack, it is not possible to declare variables of the same type as the stack itself, so a pointer must be used instead.

When the program begins, the top pointer should have a value of NULL to indicate that the stack is empty. As elements are added to the stack, the top pointer will be updated to point to the newest element.

Defining Functions to Work with the Stack

In order to add and remove elements from the stack, we need to define several functions that will interact with the stack pointer. The first function we will define is the push function, which adds a new element to the top of the stack.

Pushing an Element to the Stack

To push a new element to the stack, we will pass in the pointer to the top of the stack as well as the data for the new element. The push function will create a new element at the top of the stack that contains the new data, and will update the top pointer to reflect the new top of the stack.


Here, we create a new pointer new_node and allocate memory for the new stack element using malloc. We then assign the new data value to the data member of the new element, and set the next pointer to point at the old top element of the stack. Finally, we update the top pointer to point at the new element, and return the updated pointer.

Popping an Element from the Stack

The next function we need to define is the pop function, which removes the top element from the stack and returns its data value.

intpop(stack_node**top){if(*top==NULL){printf("Error: Cannot pop from an empty stack\n");exit(1);}intdata=(*top)->data;stack_node*temp=*top;*top=(*top)->next;free(temp);returndata;}

Here, we first check if the stack is empty, and exit the program if it is. We then get the data value from the top element, save a temporary pointer to the top element, update the top pointer to point to the next element in the stack, free the memory of the old top element using free, and finally return the saved data value.

Getting the Top Element of the Stack

Finally, we need a function to retrieve the data value of the top element of the stack without removing it. This function will simply return the value of the data member of the top element.

intpeek(stack_node*top){if(top==NULL){printf("Error: Cannot peek at an empty stack\n");exit(1);}returntop->data;}

Here, we first check if the stack is empty and exit the program if it is. We then return the value of the data member of the top element.

The Data Stack and Its Functions

The Data Stack is a fundamental data structure used in computer science and programming. It works based on the Last-In-First-Out (LIFO) principle, meaning that the last element inserted into the stack will be the first element to be removed. In this article, we will discuss the process of adding and extracting objects from a stack by creating a few necessary functions.

Adding Objects to the Stack

To add an object to the stack, we need to perform a series of steps:

  1. Take the value of the pointer, called PTR, pointing to the current object in the stack.
  2. Copy the value of Data to the next object, which Next is pointing to.
  3. Move the Next pointer to the next object in the stack.
  4. To point to the new object as being the top of the stack, update the Top pointer to reference the new object.

Suppose we execute the Push function sequentially, adding objects of value 2, 3, and 4. In that case, the stack will look like this:

4 -> Top

Extracting Objects from the Stack

To extract an object from the top of the stack, we use the Pop function. It requires an input parameter - a pointer to the top object in the stack, which we mark as PoppedObject.

  1. Check if the top object PoppedObject exists. If it does not, return NULL.
  2. Update the Top pointer to point to the next object in the stack.
  3. Return the Next pointer of the previous top object, which now becomes the new top of the stack.

Below is the code for the Pop function:


Extracting Data from a Stack

When it comes to extracting data from a stack, we need to start from the top. If there is no top object, we simply return the pointer to top.

However, if the top object exists, we'll write a function here to extract it. This is done so that we can see that the object is actually being removed and extracted. We display the following information after extraction: "The object is being removed with a percentage of 'Ed/Slashn' and these are the data that are being extracted."

To remove the object, we create a temporary pointer called "patternNext", which refers to the next objects in the stack. We set "top -> next" to patternNext and free the memory that is currently occupied by the pointer to top. We then return the address of the next object with "return PTR next".

In summary, the following steps can be taken to extract data from a stack:

  1. Check if a top object exists
  2. Write a function to extract the top object
  3. Display information about the extracted data
  4. Create a temporary pointer to refer to the next objects in the stack
  5. Set "top -> next" to patternNext and free the memory currently occupied by "top".
  6. Return the address of the next object with "return PTR next".

By following these steps, we can efficiently extract data from a stack.

Implementation of Functions for Stack Data Structure in Python

In this article, we will discuss the implementation of two functions for the stack data structure in Python. The first function, called "pop_all," will pop all the objects from our stack sequentially. The second function, called "show," will display all the objects in our stack in order starting from the top.

Pop All Function

Firstly, let's take a look at the pop_all function. We will use this function to sequentially remove all objects from our stack. We will implement the function in the following way:

  • Begin a loop called "Wild" while the top of the stack is not equal to zero.
  • Inside this loop, call the "pop" function one-by-one until all objects have been removed from the stack.

When we run our program, we can observe the function in action. We can see that the popall function removes the objects from the stack in reverse order of their addition. For example, if we added the objects 1, 2, 3, and 4 in that order, the popall function would remove them in reverse order: 4, 3, 2, 1.

Show Function

Next, we will discuss the show function, which displays all the objects in our stack. We will implement this function as follows:

  • The function will take a reference to the top of our stack as a parameter.
  • We will create a temporary pointer that will iterate through the objects in our stack.
  • Using a while loop, we will iterate through the objects in our stack by following the "Next" pointers from each object to the next.
  • Inside the loop, we will print out the "Data" field of each object in our stack.

Once we have implemented the show function, we can call it and observe the objects in our stack being printed out in reverse order, starting from the top.

Overall, these two functions provide basic functionality for a stack data structure implementation in Python. With these functions, we can add objects to our stack, remove objects sequentially, and display all objects in the stack in order.

Implementing a Stack in C

If you're a programmer, you've likely heard of stacks before. A stack is a fundamental data structure that is used in a variety of algorithms to store and retrieve data in a specific order. If you're familiar with C language, you can easily implement your own stack!

Creating the Stack

1. Defining the Stack Structure

The first step in creating a stack in C is to define the structure of the stack. We can define the stack structure using a structure in C language. We need to define two variables in the stack structure – one to track the top and another to keep track of the size of the stack.

#define MAX_SIZE 100typedefstructStack{inttop;intarr[MAX_SIZE];}Stack;

2. Initializing the Stack

After defining the structure, we need to initialize the stack that we have just created. In order to do that, we need to assign an initial value to the top variable.


3. Pushing elements to the Stack

To push elements to the stack, we need to increment the top variable and add the element to the arr variable at the top index.

voidpush(Stack*stack,intelement){if(stack->top==MAX_SIZE-1){printf("Error: Stack overflow\n");return;}stack->arr[++stack->top]=element;}

4. Popping elements from the Stack

To implement the pop function in the stack, we need to first check if the stack is empty. If it is empty, we must return the error message "stack underflow." If the stack is not empty, we can remove the element from the top of the stack.

intpop(Stack*stack){if(stack->top==-1){printf("Error: Stack underflow\n");return-1;}returnstack->arr[stack->top--];}

Using the Stack

Now that we have implemented all the stack functions, we can use them easily. We can create an instance of Stack and push elements to it. After pushing elements to the stack, we can call the pop function to remove elements from the stack.

1. Adding Elements to the Stack


2. Removing Elements from the Stack

while(myStack.top!=-1){printf("%d ",pop(&myStack));}

The output of this program will be:


Now that we have defined the structure of the stack, we are ready to implement our stack program! stay tuned for the next part of this article, where we will walk through the code step by step.
Using pointers can simplify the implementation of a stack data structure, but it is important to keep in mind the limitations and nuances of using pointers in a stack. by following the guidelines outlined here, you can create a functional and efficient stack implementation using pointers.
Understanding the data stack's mechanics and functions is crucial in programming because it is a basic yet powerful data structure that has many applications. by implementing functions such as push and pop, we can perform operations on the stack efficiently.

As you can see, implementing a stack in C is relatively simple. By following the above outlined steps, you can easily create your own stack that you can use in your programs. Stacks are a fundamental data structure in computer science and can be used in a variety of applications, so it's important to know how to implement them.

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