casting void to bool

// Long story short: Ball gets stuck against the ceiling / floor sometimes and oscillates //quickly. Was hoping this new code would correct the problem, but the line:

//bool collided = CheckWallHit(); draws the error:

//"cannot convert type 'void' to target type 'bool'"

//So how can I make this work?

/////////// New Code

        public void UpdatePosition()
        {
            size.X = (int)position.X;
            size.Y = (int)position.Y;
            oldPos.X = position.X;
            oldPos.Y = position.Y;
            position.X += speed * (float)Math.Cos(direction);
            position.Y += speed * (float)Math.Sin(direction);
            bool collided = CheckWallHit();
            if (collided)
            {
                position.X = oldPos.X + speed * (float)Math.Cos(direction);
                position.Y = oldPos.Y + speed * (float)Math.Sin(direction);
            }
        }

///////////// Old Code

        public void UpdatePosition()
        {
            size.X = (int)position.X;
            size.Y = (int)position.Y;
            position.X += speed * (float)Math.Cos(direction);
            position.Y += speed * (float)Math.Sin(direction);
            CheckWallHit();
        }


/////////// Check Wall Hit

     // Checks for collision with the ceiling or floor.
        // 2*Math.pi = 360 degrees
        // TODO: Change collision so that ball bounces from wall after getting caught
        private void CheckWallHit()
        {
            while (direction > 2 * Math.PI)
            {
                direction -= 2 * Math.PI;
            }

            while (direction < 0)
            {
                direction += 2 * Math.PI;
            }

            if (position.Y <= 0 || (position.Y > resetPos.Y * 2 - size.Height))
            {
                direction = 2 * Math.PI - direction;
            }
        }