Stack.md

Stack

The stack is a LIFO (Last In First Out) queue, which means that each element added to it gets "stacked on top" of it, and when removing it gets taken away from there. It has two main operations:

• push: add element on top of stack
• pop: remove and return element at the top of the stack

![[images/stack.png|500]]

Example code below:

#include <stdio.h>
#include <ctype.h>

#define MAX_LENGTH 100
#define EMPTY -1
#define FULL (MAX_LENGTH -1)

typedef struct {char s[MAX_LENGTH]; int top;} stack;

void reset(stack *stk) {stk->top = EMPTY;}

void push(stack *stk, char c)
{
   stk->top++;
   stk->s[stk->top] = c;
}

char pop(stack *stk) {return (stk->s[stk->top--]);}
char top(const stack *stk) {return (stk->s[stk->top]);}

int is_empty(const stack *stk) {return (stk->top == EMPTY);}
int is_full(const stack *stk) {return (stk->top == FULL);}

int main(void)
{
   stack test_stack;
   char *s = "test string";
   reset(&test_stack);
   int i = 0;
   while (s[i] != '\0')
   {
       push(&test_stack, s[i++]);
   }
   while (!is_empty(&test_stack))
   {
       printf("%c", pop(&test_stack));
   }
   printf("\n\n");
   return 0;
}