Stacks

Stacks are dynamic sets whose delete operation removes the most recently inserted element: stacks are last-in, first out (LIFO).

Stacks get their name (and or inspiration) from spring-loaded stacks of plates found in cafeterias.

Stacks have a top attribute, which is the index of the most recently inserted element, and a size attribute, which specifies the maximum size of the underlying array. When top equals zero the stack is empty.

struct Stack {
  int size, top;
  int array[STACK_SIZE];
};

bool stack_empty(struct Stack s) {
  return (s.top == 0); 
}

int push(struct Stack s, int x) {
  if (s.top == s.size)
    return 0;
  else {
    s.array[++s.top] = x;
    return 1;
  }
}

int pop(struct Stack s) {
  if (stack_empty(s))
    return 0; // Or otherwise signal an error
  else
    return s.array[s.top--];
}