The best overloaded method match for `UnityEngine.Physics.Raycast(UnityEngine.Ray, out UnityEngine.RaycastHit)' has some invalid arguments

Hi I was converting my script from js and I got this error.

Assets/weapon.cs(49,16): error CS1502: The best overloaded method match for `UnityEngine.Physics.Raycast(UnityEngine.Ray, out UnityEngine.RaycastHit)' has some invalid arguments.

Here is my script.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;

 public class weapon : MonoBehaviour {

 public int dammage = 50;
 public float distance;
 public float maxdistance = 1.5f;
 public Animator animator;
 public float damagedelay = 0.6f;
 public int hit1streak = 0;
 public int hit2streak = 0;
 public Ray ray; 


 // Update is called once per frame
 void Update () 
 {
     if(Input.GetButtonDown ("Fire1"))
         {
             attackdamage();
         }
     
 }
 IEnumerator attackdamage()
 {
     if (Random.value >= 0.5 && hit1streak <= 2) {
         animator.SetBool ("Swing01", true);
         hit1streak += 1;
         hit2streak = 0;
     } 
     else 
     {
         if (hit2streak <= 2) {
             animator.SetBool ("Swing02", true);
             hit1streak = 0;
             hit2streak += 1;
         } 
         else {
             animator.SetBool ("Swing01", true);
             hit1streak += 1;
             hit2streak = 0;
         }
     }
             yield return new WaitForSeconds(damagedelay);
             RaycastHit hit;
              ray = Camera.main.ScreenPointToRay (new Vector3(Screen.width/2, Screen.height/2,0));
             if(Physics.Raycast (ray, hit))
             {
                 distance = hit.distance;
                 if(distance < maxdistance)
                 {
                     hit.transform.SendMessage ("applydammage", dammage, SendMessageOptions.DontRequireReceiver);
                 }

             }
             animator.SetBool ("Swing01", false);
             animator.SetBool ("Swing02", false);
     
 }

}