/** This class provides methods that are useful for
 *  processing mathematical expressions as strings.
 *
 *  @author Adam Blank
 */
public class EvaluatorUtilities {
	
	/** Returns true if the given string can be interpreted
	 *  as a number, false otherwise.
	 */
    public static boolean isNumber(String x) {
        for (int i = 0; i < x.length(); i++) {
            if (x.charAt(i) < '0' || x.charAt(i) > '9') {
                return false;
            }
        }
        return true;
    }

    /** Returns the index in the given string of the next operator to be
     *  evaluated.  <br> Returns -1 if there is no operator in exp.<br><br>
     *  
     *  For example, if exp is "(((1+2)*3)+(4*2))", nextOperator
     *  would return 10, because the "+" is the outermost operator
     *  and should be evaluated next.<br><br>
     *  
     *  This method considers "+", "*", "^", and "-" to be operators.
	 */
    public static int nextOperatorIndex(String exp) {
        int parens = 0;
        for (int i = 0; i < exp.length(); i++) {
            char c = exp.charAt(i);
            if (c == '(') {
                parens++;
            }
            else if (c == ')') {
                parens--;
            }
            if (parens == 0 && (c == '+' || c == '*' || c == '^' || c == '-')) {
                return i;
            }
        }
        return -1;
    }
    
    /** Returns a character representing the next operator in
     *  the given string. <br> Returns '?' if there is no such operator.<br><br>
     * 
     *  See {@link #nextOperatorIndex(String) nextOperatorIndex} for more description of 'next'
     *  and 'operator'.
     */
    public static char nextOperator(String exp) {
    		int opIndex = nextOperatorIndex(exp);
    		if (opIndex == -1) {
    			return '?';
    		}
    		return exp.charAt(nextOperatorIndex(exp));
    }
}

class NotImplementedException extends Exception {
	private static final long serialVersionUID = 1L;
}