Unity3d Character Move

public class Movement : MonoBehaviour {
	public float _rotationSpeed;
	public float _moveSpeed;
	private bool isGrounded = false;
	// Use this for initialization
	void Start () {
		print(Vector3.up);
	}
	
	// Update is called once per frame
	void Update () {
		if(Input.GetKey(KeyCode.A)){
			transform.Rotate(Vector3.down * Time.deltaTime * _rotationSpeed);
		}
		if(Input.GetKey(KeyCode.D)){
			transform.Rotate(Vector3.up * Time.deltaTime* _rotationSpeed);
		}
		if(Input.GetKey(KeyCode.Space) && isGrounded == true){
			rigidbody.AddForce(Vector3.up * 100);
		}
		if(Input.GetKey(KeyCode.W)){
			transform.position += transform.forward * _moveSpeed * Time.deltaTime;
		}
		if(Input.GetKey(KeyCode.S)){
			transform.position += transform.forward * -_moveSpeed * Time.deltaTime;
		}
		
	}
	void OnCollisionEnter(Collision col){
		if(col.transform.tag == "Floor"){
			isGrounded = true;
			print("Enter Floor");
		}
	}
	void OnCollisionExit(Collision col){
		if(col.transform.tag == "Floor"){
			isGrounded = false;
			print("Leave Floor");
		}
	}
}