import java.util.Stack;


public class Implementation implements Calculator {

	String [] list = new  String [1000] ;
	int size = 0 ;
	int index = -1 ;

	@Override
	public void Input(String s) {
		// TODO Auto-generated method stub
		index++;
		list[index] = s ;
		size++;

	}

	@Override
	public String current_formula() {
		// TODO Auto-generated method stub

		String up = END_LIST_UP ;
		String down = END_LIST_DOWN ;
		if (index < 0) return up;
		if (index >= size) return down;
		return list[index];
	}

	@Override
	 public String getResults() {
		// TODO Auto-generated method stub

		GetResults answer = new GetResults (list[index]) ;
		String d = Double.toString(answer.l);
		return d;
	}

	@Override
	public void save() {
		// TODO Auto-generated method stub

	}

	@Override
	public void load() {
		// TODO Auto-generated method stub

	}

	@Override
	public String prev() {
		// TODO Auto-generated method stub

		index-- ;
		String ret = current_formula() ;
		if(index < 0) index++ ;
		return ret ;
	}

	@Override
	public String next() {
		// TODO Auto-generated method stub

		index++ ;
		String ret = current_formula() ;
		if(index >=  size ) index-- ;
		return ret ;
	}

}