public class OurStack {

    char[] letters;         // Store the chars in here.
    int top;                // letters[top]: next available space.


    // Constructor.

    public OurStack ()
    {
	letters = new char [100];
	top = 0;
    }


    public void push (char ch)
    {
        // Test for full stack.
        if (top >= letters.length) {
            System.out.println ("ERROR: OurStack.push(): stack overflow");
            return;
        }
        
	letters[top] = ch;
	top ++;
    }


    public char pop ()
    {
        // Test for empty stack.
	if (top <= 0) {
            System.out.println ("ERROR in OurStack.pop(): stack empty");
            // Still need to have a return statement, so we return some "junk letter".
            return '@';
	}

        top --;
        return letters[top];
    }


    public boolean isEmpty ()
    {
	if (top == 0) {
	    return true;
	}
	else {
	    return false;
	}
    }

}