Stack

Stack is an LIFO (Last In First Out) data structure.

Stack is a linear data structure where insertion and deletion operations are performed from one end called TOP. A TOP is a pointer which points to the top element- the element which entered last in the stack.

Stack can be implemented with an array and a linked list. Here, We will see the implementation of stack using array in C with basic operations on stack.

Basic Operations on Stack

PUSH
POP

Insertion of element in the stack is called as PUSH and Deletion of element from the stack is called POP operation.

Algorithm:

PUSH(Stack, N, Item)

This algorithm will insert Item at top to Stack having size N. Here initial index for stack is 0.

           if TOP >= N - 1 then
                     "Overflow"
           else
                     TOP = TOP + 1
                     Stack[TOP] = Item

PUSH Operation on Stack

POP(Stack, N)

This algorithm will delete the top element from the Stack having size N. Here initial index for stack is 0.

  if TOP = -1 then   
           "Underflow"
  else
            Stack[TOP] = NULL
            TOP = TOP - 1

POP Operation on Stack

Implementation of Stack using array in C program with PUSH and POP operations :

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#include <stdio.h>
#include <conio.h>

#define N 5
int top = -1;
int stack[N];

//Function prototypes
void push(int item);
int pop();

void main()
{
      int item, choice, cont = 1;
      clrscr();

while(cont == 1)
      {
            printf("\n1.Push onto stack.\n");
            printf("\n2.Pop from stack.\n");

printf("\nEnter your choice: ");
            scanf("%d",&choice);

switch(choice)
            {
                  case 1:
                        printf("\nEnter the value of item:");
                        scanf("%d",&item);
                        push(item);
                        break;
                  case 2:
                        item = pop();
                        if(item != NULL)
                        {
                            printf("\nItem popped out: %d\n",item);
                        }                       
                        break;
                  default:
                        printf("\nInvalid choice.\n");
                        break;
            }
            printf("\nDo you want to continue (1/0): ");
            scanf("%d",&cont);
      }
      getch();
}

//Function Definition for push operation
void push(int item)
{
      if(top >= N-1)
      {
            printf("\nStack Overflow. Push not possible.\n");
      }
      else
      {
            top = top+1;
            stack[top] = item;
      }
}

//Function for pop operation
int pop()
{
      int item = NULL;

if(top == -1)
      {
            printf("\nStack Underflow. Pop not possible.\n");
      }
      else
      {
            top = top-1;
            item = stack[top+1];
            stack[top+1]=NULL;
      }
      return(item);
}

Output :

1.Push onto stack.
2.Pop from stack.
Enter your choice: 1
Enter the value of item:10
Do you want to continue (1/0): 1

1.Push onto stack.
2.Pop from stack.
Enter your choice: 1
Enter the value of item:20
Do you want to continue (1/0): 1

1.Push onto stack.
2.Pop from stack.
Enter your choice: 11
Enter the value of item:30
Do you want to continue (1/0): 1

1.Push onto stack.
2.Pop from stack.
Enter your choice: 2
Item popped out: 30
Do you want to continue (1/0): 1

1.Push onto stack.
2.Pop from stack.
Enter your choice: 1
Enter the value of item:40
Do you want to continue (1/0): 1

1.Push onto stack.
2.Pop from stack.
Enter your choice: 1
Enter the value of item:50
Do you want to continue (1/0): 1

1.Push onto stack.
2.Pop from stack.
Enter your choice: 1
Enter the value of item:60
Do you want to continue (1/0): 1

1.Push onto stack.
2.Pop from stack.
Enter your choice: 1
Enter the value of item:70
Stack Overflow. Push not possible.
Do you want to continue (1/0): 1

1.Push onto stack.
2.Pop from stack.
Enter your choice: 2
Item popped out: 60
Do you want to continue (1/0):0

Find Material Here:

Solved Infix to Prefix and Infix to Postfix Examples

Infix to Postfix conversion using Stack with C Program and Algorithm

Important Question Answers of Stack

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