// Subtract 'num' from me in my base, returning the new value.
    // Precondition: my number >= 'num'.
    // ------------------------------------------------------------------
    // STUDENTS WILL WRITE THIS METHOD.
    private NIB subtract (NIB num) {
 
        // Start the result as the number being subtracted from.
        NIB res = new NIB(toString(), getBase());
 
        // The index of the current characters being subtracted.
        int i = 0;
 
        // While there are digits to subtract...
        while (i < res.getNumDigits()) {
 
            // If a(i) < b(i), we need to perform a carry.
            if (res.digits[i] < num.digits[i]) {
 
                res.digits[i] += res.getBase();
                res.digits[i+1] --;
                }
 
            res.digits[i] -=  num.digits[i];
            i++;
        }
 
        // Deal with any leading 0's and update the size of the number.
        while (i > -1 && res.digits[i] == 0) {
            i--;
        }
        res.setNumDigits(i+1);
 
        return res;
    }
 
 
    // Return a new NumberInBase in base 'b' whose value is equivalent to
    // mine.
    // ------------------------------------------------------------------
    // STUDENTS WILL WRITE THIS METHOD.
    public NIB convertTo (int b) {
 
        // For the result.
        NIB numberInNewBase = new NIB("",b);
        NIB workspace = new NIB(toString(),getBase());
        NIB divisor =
            new NIB(Integer.toString(b,getBase()),getBase());
 
        int count = 0;
 
        while (Integer.parseInt(workspace.toString(),
                workspace.getBase()) != 0) {
 
            int rem = workspace.remainder(divisor);
            numberInNewBase.putDigit(rem,count);
            workspace = workspace.divide(divisor);
            count ++;
        }
 
        return numberInNewBase;
 
    }