package test5;

public class Test5A 
{
    /**
     * Returns the sum of the digits of the given string.
     * The sum of the empty string is 0.
     * 
     * @param digits a string consisting of only digits.
     * @pre. digits consists of only digits.
     * @return the sum of the digits of the given string.
     */
    public static int sum(String digits)
    {
	int sum;
	if (digits.length() == 0)
        {
    	    sum = 0;
	}
	else
	{
	    sum = (digits.charAt(0) - '0') + Test5A.sum(digits.substring(1));
	}
	return sum;
    }
    
    /**
     * Tests whether the given character occurs an even number of 
     * times in the given string.  The number 0 is even.
     * 
     * @param word a word.
     * @pre. word != null
     * @param character a character
     * @return true if the given character occurs an even number of 
     * times in the given string, false otherwise.
     */
    public static boolean even(String word, char character)
    {
	boolean even;
	if (word.length() == 0)
	{
	    even = true;
	}
	else
	{
	    if (word.charAt(0) == character)
	    {
		even = !Test5A.even(word.substring(1), character);
	    }
	    else
	    {
	        even = Test5A.even(word.substring(1), character);
	    }
	}
	return even;
    }
}