Stack example in C.

main.c

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

typedef struct stack_item
{
  // The value given to the item.
  int value;
  // The pointer to the previous item.
  struct stack_item * prev;
} stack_item;

typedef struct stack
{
 // The current length of the stack.
 int length;
 // The head is a pointer to the value at the top of the stack.
 stack_item * head;
} stack;

stack * create_stack()
{
  stack * s = (stack *) malloc(sizeof(stack));
  s->length = 0;
  s->head = NULL;
  return s;
}

void stack_push(stack * s, int value)
{
  stack_item * si = (stack_item *) malloc(sizeof(stack_item));
  si->value = value;
  si->prev = s->head;
  s->head = si;
  s->length++;
}

int stack_pop(stack * s)
{
  // Get the value from the current item before we remove it.
  int value = s->head->value;

  stack_item * i = s->head;
  // Set head on the stack to the previous item.
  s->head = s->head->prev;
  // Decrement the size of the stack.
  s->length--;
  // Free up the memory allocated for the previous item.
  free(i);
  // Return the value we stored from the item we removed.
  return value;
}

int main() {
  stack * s = create_stack();

  stack_push(s, 1);
  stack_push(s, 2);
  stack_push(s, 3);

  printf("First: %d\n", stack_pop(s));
  printf("Second: %d\n", stack_pop(s));
  printf("Third: %d\n", stack_pop(s));

  return 0;
}