C Stack Operations using Linked List

Stack

A stack is a data structure in which addition of new element or deletion of existing element are always take place at the top of the stack.

Last In First Out (LIFO).

Linked list are not stored in adjacent locations and array occupy continuous locations.

C Program to Implement Queue and Operations using Linked List

#include<stdio.h>  

//structure contains data and link
struct node
{
    int data;
    struct node *link;
};

//Adding element in the stack on top
void push(struct node **top, int data)
{
    struct node *temp;

    temp = malloc( sizeof (struct node));
    temp->data = data;
    temp->link =*top;
    *top = temp;
}

// displays the stack elements from top
void display(struct node *head)
{
    printf("\n");
    // traversing entire linked list
    printf("\ntop==>");
    while(head != NULL)
    {
        printf("%d-->", head->data);
        head = head->link;
    }
    printf("bottom\n");
}

// finds the number of elements in the stack
int count(struct node *head)
{
    int c = 0;
    while(head != NULL)                                                         
    {                                                                           
        head = head->link;          
        c++;
    } 
    return c;
}

// deletes the top element in stack
int pop(struct node **top)
{
    int data;
    struct node *old, *temp;
    if(*top == NULL)
    {
        printf("\ntop is empty!");
    }
    else
    {
        temp = *top;
        data = temp->data;
        *top = temp->link;
        free(temp);
        return data;
    }
    return 0;
}


void main()                                                                     
{       
    int op, data;
    struct node *top;                                                           
    // Empty top
    top = NULL;                                                                 
                                                                                
    printf("\nNumber of elements in the top: %d", count(top));          
    push(&top, 1);                                                            
    push(&top, 2);                                                            
    push(&top, 3);                                                            
                                                                                
    display(top);       
    printf("\nNumber of elements in the top: %d", count(top));

    do
    {
        printf("\nStack\n---------------\n1.push \n2.pop\n3.display\n4.count\n0.exit");
        printf("\nEnter choice: ");
        scanf("%d", &op);
        switch(op)
        {
            case 1:
                printf("\nEnter element: ");                                    
                scanf("%d", &data);                                             
                push(&top, data);
                break;
            case 2:
                printf("popped up: %d", pop(&top));  
                break;
            case 3:
                display(top);
                break;
            case 4:
                printf("\nNumber of elements in the linked list: %d", count(top));
                break;
        }
    }while(op>=1 && op<=4);
}                                                                                                                                                                                                                                                                                                                                                                     

$ cc stack.c 
stack.c: In function ‘push’:
stack.c:14:12: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration]
     temp = malloc( sizeof (struct node));
            ^~~~~~
stack.c:14:12: warning: incompatible implicit declaration of built-in function ‘malloc’
stack.c:14:12: note: include ‘’ or provide a declaration of ‘malloc’
stack.c: In function ‘pop’:
stack.c:57:9: warning: implicit declaration of function ‘free’ [-Wimplicit-function-declaration]
         free(temp);
         ^~~~
stack.c:57:9: warning: incompatible implicit declaration of built-in function ‘free’
stack.c:57:9: note: include ‘’ or provide a declaration of ‘free’

$ ./a.out 

Number of elements in the top: 0

top==>3-->2-->1-->bottom

Number of elements in the top: 3
Stack
---------------
1.push 
2.pop
3.display
4.count
0.exit
Enter choice: 1

Enter element: 3

Stack
---------------
1.push 
2.pop
3.display
4.count
0.exit
Enter choice: 3


top==>3-->3-->2-->1-->bottom

Stack
---------------
1.push 
2.pop
3.display
4.count
0.exit
Enter choice: 4

Number of elements in the linked list: 4
Stack
---------------
1.push 
2.pop
3.display
4.count
0.exit
Enter choice: 2
popped up: 3
Stack
---------------
1.push 
2.pop
3.display
4.count
0.exit
Enter choice: 3


top==>3-->2-->1-->bottom

Stack
---------------
1.push 
2.pop
3.display
4.count
0.exit
Enter choice: 1

Enter element: 5

Stack
---------------
1.push 
2.pop
3.display
4.count
0.exit
Enter choice: 3


top==>5-->3-->2-->1-->bottom

Stack
---------------
1.push 
2.pop
3.display
4.count
0.exit
Enter choice: 0