Explain the concept of stack in C language

Data structure is a collection of data organised in a structured way. It is classified into two types which are linear data structure and non-linear data structure.

Linear data structure − Here, data is organised in a linear fashion.

For example − Arrays, structures, stacks, queues, linked lists.

Non-linear data structure − Here, Data is organised in a hierarchical way.

For example − Trees, graphs, sets, tables.

Stack in C language

It is a linear data structure, where data is inserted and removed only at one end.

Operations

• Push – Inserting an element into a stack.
• Pop – Deleting an element from a stack.

Deleted element = 50
Item = a [top]
top --

• pop() ,pop(),pop(), pop()

Deleted element = 40
Deleted element=30
Deleted element=20
Deleted element =10

• Pop ( )

Stack under flow

Conditions

• Stack over flow − Trying to insert an element into a full stack.

• Stack under flow − Try to delete an element from a stack which is empty.

Algorithms for Push ( ), Pop ( ) , Display ( )

The respective algorithms are as follows −

Push ( )

• Check for stack overflow.

if (top = = n-1)
printf("stack over flow”);

• Otherwise, insert an element into the stack.

top ++
a[top] = item

Pop ( )

• Check for stack underflow.

if ( top = = -1)
printf( "stack under flow”);

• Otherwise, delete the element from the stack.

item = a[top]
top --

Display ( )

• Check for stack flow.

if (top == -1)
printf ("stack is empty”);

• Otherwise, follow the below mentioned algorithm −

for (i=0; i<top; i++)
printf ("%d”, a[i]);

Example

Following is the C program for implementation of stack by using the arrays −

#include<stdio.h>
#include <conio.h>
int top = -1, n,a[100];
main ( ){
   int ch;
   void pop ( );
   void display ( );
   clrscr ( );
   printf ("enter the size of the stack”);
   scanf ("%d”, &n);
   printf("stack implementation
”);
   printf ("1. push 
”);
   printf ("2. Pop 
”);
   printf ("3. exit 
”);
   do{
      printf ( "enter ur choice”);
      scanf ("%d”, &ch);
      switch (ch){
         case 1 : push ( );
         display ( );
         break;
      case 2 : push ( );
         display ( );
         break;
      case 3 : exit
   }
   }while (ch>=1 | | ch<= 3);
   getch ( );
}
void push ( ){
   int item;
   if (top = = n-1)
      printf ( "stack over flow”)
   else{
      printf("enter an element for insertion”)
      scanf ("%d”, &item);
      top ++;
      a[top] = item;
   }
}
void pop ( ){
   int item;
   if (top = = -1);
      printf ( "stack under flow”);
   else{
      item = a[top];
      top --;
      printf("deleted element = %d”, item);
   }
}
void display ( ){
   int i;
   if (top = = -1)
      printf ( "stack is empty”);
   else{
      printf("contents of the stack are”);
      for (i=0; i<top; i++)
         printf ("%d \t”, a[i]);
   }
}

Output

When the above program is executed, it produces the following result −

enter the size of the stack = 5 [given by user]
Stack implementation
1. Push 2. Pop 3. exit
Enter ur choice : 1 [given by user]
Enter an element for insertion : 10
Contents of the stack : 10
Enter ur choice : 1
Enter an element for insertion : 2
Contents of the stack : 10 20
Enter ur choice : 2
Deleted element = 20
Contents of the stack are : 10
Enter ur choice : 2
Deleted element : 10
Contents of the stack are : stack is empty
Enter ur choice : 2
Stack underflow.
Enter ur choice : 1
Enter an element for insertion : 30
Contents of the stack are : 30