// Stack implemented as a linked list -- Pouya Larjani

typedef char* element;              // Type of elements in the stack

typedef struct node_s* node;        // Stack node (pointer) type
struct node_s {                     // Node structure
    element data;                   // Current node's data
    node below;                     // Pointer to the node below this one
};

typedef struct stack_s* stack;      // Stack (pointer) type
struct stack_s {                    // Stack structure
    node top;                       // Top node of the stack
    int height;                     // Height of the stack
};

stack bottom();                     // Make a new stack
int height(stack s);                // Height of the stack
element top(stack s);               // Top element of the stack
void pop(stack s);                  // Pop the top element of a stack
void push(stack s, element data);   // Push an element to the top of the stack
void print_stack(stack s);          // Print a stack