What is Stack

STACK

 

A stack is a data structure that follows the last in, first out (LIFO) principle, where the last element added to the stack is the first element removed. This means that elements are added to and removed from the same end, usually known as the "top" of the stack.

 

Basic Operations on a Stack:

1. Push: Adds an element to the top of the stack.

2. Pop: Removes the element from the top of the stack.

3. Peak or Top: Returns the element to the top of the stack without removing it.

4. isEmpty: Checks whether the stack is empty or not.

5. Size: Returns the number of elements in the stack.

 

    Types of Stacks:

1. Fixed-size stack: A stack with a predetermined size that cannot be changed during runtime.

2. Dynamic Stack: A stack that can grow or shrink dynamically depending on the program's needs.

 

Applications of Stacks:

1. Function Call Management: Most programming languages use stacks to manage function calls. When a function is called, its return address and local variables are pushed onto the stack. When the function completes, these values are popped off the stack.

2. Expression Evaluation: The stack is used to evaluate expressions, especially in converting infix expressions to postfix or prefix forms. They help maintain the order of operations.

3. Undo Mechanism: Stacks are employed in undo mechanisms in applications. Each action that can be undone is typically pushed onto a stack, and the undo operation pops the last action of the stack.

4. Backtracking Algorithms: Stacks are used in backtracking algorithms, where the system needs to keep track of decisions made so that it can explore alternative decisions if necessary.

 

5. Parsing and Syntax Analysis: Stacks are used in parsing and syntax analysis of programming languages. They help in tracking the structure of expressions and ensuring proper nesting of symbols.

 

6. Memory Management: Stacks are used in managing memory in computer systems. The call stack, for example, is used to store function call information.

 

7. Undo/Redo Mechanisms in Software Applications: Stacks are often used to implement undo and redo functionality in applications, allowing users to reverse or redo their recent actions.

Example in C language:

1.  #include <stdio.h>
2. #include <stdlib.h>
3. 
   
4. #define MAX_SIZE 10
5. 
   
6. typedef struct {
7.     int items[MAX_SIZE];
8.     int top;
9. } Stack;
10. 
    
11. void initialize(Stack *stack) {
12.     stack->top = -1;
13. }
14. 
    
15. int is_empty(Stack *stack) {
16.     return stack->top == -1;
17. }
18. 
    
19. int is_full(Stack *stack) {
20.     return stack->top == MAX_SIZE - 1;
21. }
22. 
    
23. void push(Stack *stack, int value) {
24.     if (!is_full(stack)) {
25.         stack->items[++stack->top] = value;
26.     } else {
27.         printf("Stack overflow: Cannot push element %d, the stack is full.\n", value);
28.     }
29. }
30. 
    
31. int pop(Stack *stack) {
32.     if (!is_empty(stack)) {
33.         return stack->items[stack->top--];
34.     } else {
35.         printf("Stack underflow: Cannot pop from an empty stack.\n");
36.         return -1; // Assuming -1 as an error value; adjust as needed
37.     }
38. }
39. 
    
40. int peek(Stack *stack) {
41.     if (!is_empty(stack)) {
42.         return stack->items[stack->top];
43.     } else {
44.         printf("Cannot peek from an empty stack.\n");
45.         return -1; // Assuming -1 as an error value; adjust as needed
46.     }
47. }
48. 
    
49. int main() {
50.     Stack stack;
51.     initialize(&stack);
52. 
    
53.     push(&stack, 1);
54.     push(&stack, 2);
55.     push(&stack, 3);
56. 
    
57.     printf("Stack: ");
58.     while (!is_empty(&stack)) {
59.         printf("%d ", pop(&stack));
60.     }
61.     printf("\n");
62. 
    
63.     return 0;
64. }

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

        #define MAX_SIZE 10

        typedef struct {
            int items[MAX_SIZE];
            int top;
        } Stack;

        void initialize(Stack *stack) {
            stack->top = -1;
        }

        int is_empty(Stack *stack) {
            return stack->top == -1;
        }

        int is_full(Stack *stack) {
            return stack->top == MAX_SIZE - 1;
        }

        void push(Stack *stack, int value) {
            if (!is_full(stack)) {
                stack->items[++stack->top] = value;
            } else {
                printf("Stack overflow: Cannot push element %d, 
                

                the stack is full.\n", value);
            }
        }

        int pop(Stack *stack) {
            if (!is_empty(stack)) {
                return stack->items[stack->top--];
            } else {
                printf("Stack underflow: Cannot pop from an empty stack.\n");
                return -1; // Assuming -1 as an error value; adjust as needed
            }
        }

        int peek(Stack *stack) {
            if (!is_empty(stack)) {
                return stack->items[stack->top];
            } else {
                printf("Cannot peek from an empty stack.\n");
                return -1; // Assuming -1 as an error value; adjust as needed
            }
        }

        int main() {
            Stack stack;
            initialize(&stack);

            push(&stack, 1);
            push(&stack, 2);
            push(&stack, 3);

            printf("Stack: ");
            while (!is_empty(&stack)) {
                printf("%d ", pop(&stack));
            }
            printf("\n");

            return 0;
        }
    

In summary, stacks are a fundamental data structure with various applications in computer science and programming due to their simplicity and efficiency in managing data with a Last-In, First-out order.

 By SHUBHAM KUMAR LABH