How to rotate snake at an exact 90 degrees

You will have to do some sort of swipe gesture detection so once an "upwards" swipe is detected that it should move up instead of wherever it was currently heading and likewise for all other directions. You will have to look into Input Touches to do this. It's not an easy task but not impossible. There are many assets on the Asset Store that do touch gesture recognition for this reason.

Since your snake is just spheres you can just change the movement direction instead of doing a real rotation.

Depending on how you want the snake movement it would change how to implement it as well. Do you want the body parts behind the head to move towards the head all the time (even when it changes direction), or do you want the body parts to take the exact full path that the head did?

Leuthil well thanks for the rapid reply. I had enabled the swipe gestures, and you can see snake moves pretty fine. but the problem is that. when i swipe up and snake's head direction is on right-it moves towards down instead of upward :(

You will have to post the code you are using to change the direction of the snake otherwise there's really no way anyone can help :).

My Update method snippet : kindly help me please

 void Update()
     {
         transform.Translate(new Vector3(0, 0, 0.09f));
 
         foreach (Touch T in Input.touches)
         {
             var P = T.position;
             if (T.phase == TouchPhase.Began && SwipeID == -1)
             {
                 SwipeID = T.fingerId;
                 StartPos = P;
             }
             else if (T.fingerId == SwipeID)
             {
                 Vector2 delta = P - StartPos;
                 if (T.phase == TouchPhase.Moved && delta.magnitude > minMovement)
                 {
                     SwipeID = -1;
                     if (Mathf.Abs(delta.x) > Mathf.Abs(delta.y))
                     {
                         if (delta.x > 0)
                         {
                                 transform.Rotate(new Vector3(0, 90, 0));
                             //    Debug.Log("Swipe Right Found");
                         }
                         else
                         {
                             transform.Rotate(new Vector3(0, -90, 0));
                           //  Debug.Log("Swipe Left Found");
                             
                         }
                     }
                     else
                     {
 
                         if (delta.y > 0)
                         {
                             transform.Rotate(new Vector3(0, 90, 0));
                             //Debug.Log("Swipe Up Found");
                         }
                         else
                         {
                             transform.Rotate(new Vector3(0, -90, 0));
                             //Debug.Log("Swipe Down Found");
                         }
 
                     }
                 }
                 else if (T.phase == TouchPhase.Canceled || T.phase == TouchPhase.Ended)
                     SwipeID = -1;
             }
         }   
         if (Time.time % 10 < 0.05)
             placeFood();
 
     }
 }

hey @ad_adnan can you give your script?