STACK

what is stack ?

Stack is an ordered list in which, insertion and deletion operations can be performed only at one end that is called top.
Stack is a recursive data structures having pointer to its top element.
Stack is also called linear data structure.
Stacks are sometimes called as Last-In-First-Out(LIFO) lists. i.e. element which inserted first in the stack will deleted last from the stack.

Application of Stack

1. Recursion
2. Expression evaluation and conversions
3. Parsing
4. Browsers
5. Editors
6. Tree traversals

Operation on stack

PUSH : Adding elements into stack
POP : Removing elements from stack

Stack program using Array 

/*stack using array
Last-In-First-Out (FIFO)
*/
#include<stdio.h>
#include<stdlib.h>
#define max 5
struct stack{
    int item[max], top;
}s;
int index;
//displaying stack elements
void display(){
    if(s.top == -1){
        printf("\nStack is empty");
    }else{
        printf("\nThe stack elements are: ");
        for(index=0;index<=s.top;index++){
            printf("%d\t",s.item[index]);
        }
    }
}
//inserting elements into stack
void push(){
    int element;
    if(s.top == (max-1)){
        printf("\nStack is full");
    }else{
        printf("\nEnter new element: ");
        scanf("%d",&element);
        s.item[++s.top] = element;
        printf("\nPUSH operation done successfully");
        display();
    }
}
//deleting element from stack
void pop(){
    if(s.top == -1){
        printf("\nStack is empty");
    }else{
        printf("\nPOP element is: %d",s.item[s.top--]);
        printf("\nPOP operation done successfully");
        display();
    }
}
//main function
int main(){
    int ch;
    while(1){
        printf("\n1.PUSH();\n2.POP();\n3.display();\nexit();\nEnter your choice: ");
        scanf("%d",&ch);
        switch(ch){
        case 1:
            push();
            break;
        case 2:
            pop();
            break;
        case 3:
            display();
            break;
        case 4:
            exit(1);
            break;
        default:
            printf("\nWrong choice, try again......");
            break;
        }
    }
}

output :