/**
 * An IntStack is an object that holds a stack of ints.
 */
public class IntStack {
  private Node top = null; // The top Node in the stack

  /**
   * Test whether this stack has more elements.
   * @return true if this stack is not empty
   */
  public boolean hasMore() {
    return (top != null);
  }

  /**
   * Pop the top int from this stack and return it.
   * This should be called only if the stack is
   * not empty.  If called when the stack is empty,
   * we print an error message and exit the program.
   * @return the popped int
   */
  public int pop() {
    Node n = top;
    if (n == null) {
      System.out.println("Popping an empty stack!");
      System.exit(-1);
    }
    top = n.getLink();
    return n.getData();
  }

  /**
   * Push an int on top of this stack.
   * @param data the String to add
   */
  public void push(int data) {
    top = new Node(data,top);
  }
}