// stack with integer values

#include "istack.h"

// The stack is implemented by having a node for the stack
// which points to the first real item of the stack.

// Initialize the stack as an empty stack
void stackInitialize(StackItem * stack) {
    stack->next = NULL;  // Initialize as empty
    // Note we don't care about data value in the control node
}

// Add the value to top of stack
void push(StackItem * stack, int n) {
    StackItem *tmp = (StackItem *)(malloc (sizeof (struct StackItem)));
    tmp->value = n;
    tmp->next = stack->next;
    stack->next = tmp;
}

// Check if stack is empty
int stackIsEmpty(StackItem * stack) {
    return stack->next == NULL ? 1 : 0;
}

// Remove and return the top value
int pop(StackItem * stack) {
    int retval = 0;
    if (!stackIsEmpty(stack)) {
        StackItem * tmp = stack->next;
        stack->next = stack->next->next;
        retval = tmp->value;
        free(tmp);
    }
    return retval;
}

// Display the stack
void stackDisplay(StackItem * stack) {
    for ( StackItem * current = stack->next;
          current != NULL;
          current = current->next ) {
        if (current != stack->next)
            printf(" ");
        printf("%d", current->value);
    }
    printf("\n");
}