In this tutorial, you will learn in-depth about the concept of stack in C programming with the relevant example.

Stack in C programming

Stack is the example of a sequential data structure. Stack is simply like books that are kept one above other. It is like a container in which objects are placed sequentially one above other.

Data in the stack are placed or removed in the principle of Last In First Out (LIFO).

Stack in memory is pointed via a pointer. Stack pointer always points to the top element in the stack.

The last node of a stack is set to NULL indicating the bottom of the stack. Therefore, we always check the stack pointer for NULL value while programming.

Function used in stack program in C

There are two primary functions used in stack operation:

• Push
• Pop

Push function is used to insert data at the top of the stack while pop removes topmost data from the stack.

A stack is a recursive data structure.

Stack program in C – Example

//Implementation of stack

#include <stdio.h>
#include<stdlib.h>

//declaring structure
struct stack
{
   int data;
   struct stack *ptr; //pointer type of stack
};

typedef struct stack Stack;
typedef Stack *stackPtr;

//function prototypes of different functions
void push(stackPtr *top, int x); //for pushing value in stack
int pop(stackPtr *top); //for popping value out of stack
int checkEmpty(stackPtr top); //checking whether stack is empty
void printValue(stackPtr showPtr); //for printing value that are pushed and popped

int main()
{
   stackPtr stackNewPtr = NULL; //declared pointer that points to the top of stack
   int option; //variable for choosing different options
   int value; //variable for storing entered by the user

   //different options for the user
   printf("\nPlease choose following options:\n");
   printf("1. PUSH\n");
   printf("2. POP\n");
   printf("3. EXIT\n");

   scanf("%d", &option);

   //program flow enters while loop if user enter value other than 3
   while (option != 3)
   {
      switch (option)
      {
      case 1:
         printf("\nEnter value: ");
         scanf("%d", &value);
         push(&stackNewPtr, value);
         printValue(stackNewPtr);
         break;

      case 2:
         if (!checkEmpty(stackNewPtr))
         {
            printf("\nPopped Value: %d\n", pop(&stackNewPtr));
         }
         printValue(stackNewPtr);
         break;

      default:
         puts("\n**Invalid choice**");
         break;
      }

      printf("\nWhat do you want: ");
      scanf("%d", &option);
   }
}

//function for pushing value into the top of stack
void push( stackPtr *top, int x )
{
    stackPtr nodePtr;

    //allocating memory
    nodePtr = malloc(sizeof(Stack));

    //pushing value at the top of stack only if there is space
    if(nodePtr != NULL)
    {
       nodePtr -> data = x;
       nodePtr -> ptr = *top;
       *top = nodePtr;
    }

    else
       printf("\nERROR !!! (Not enough space)");
   }

//popping value out of the stack
int pop(stackPtr *top)
{
   int pValue; //variable for value at the top
   stackPtr tempPtr; //temporary pointer

   tempPtr = *top;
   pValue = (*top) -> data;
   *top = (*top) -> ptr;
   free(tempPtr); //free temporary pointer value
   return pValue;
}

//function for printing value stored in the stack
void printValue(stackPtr showPtr)
{
   if(showPtr == NULL)
   {
       printf("\nNo value found.");
   }
   else
   {
      printf("\nData stored in stack:\n");

      while(showPtr != NULL)
     {
         printf("%d --> ", showPtr -> data);
         showPtr = showPtr -> ptr;
     }
     printf("NULL\n");
   }
}

int checkEmpty(stackPtr top)
{
   return top == NULL;
}

Output

#1

#2