int guess_rec_c( int ans, int lower, int higher ) {
    int guess;
    guess = (int)((lower + higher)/2);
    if (ans == guess) return guess;
    if ( guess > ans ) {
         return guess_rec_c( ans, lower, guess -1 );
    }
    else {
         return guess_rec_c( ans, guess +1, higher );
    }
}