Help me error cs0131

i got an error on this(error CS0131: The left-hand side of an assignment must be a variable, a property or an indexer (if ((float)blockPos.y = 0) return;))
But i dont know the problem please help me.

void Update ()
    	{
    		if (Input.GetMouseButtonDown (0)) 
    		{
    			RaycastHit hit;
    			Ray ray = Camera.main.ScreenPointToRay (new Vector3 (Screen.width / 2.0f, Screen.height / 2.0f, 0));
    			if (Physics.Raycast (ray, out hit, 1000.0f)) 
    			{
    				Vector3 blockPos = hit.transform.position;
    				//bedrock
    				if ((int)blockPos.y = 0) return;
    
    				worldBlock[(int)blockPos.x,(int)blockPos.y,(int)blockPos.z] = null;
    
    				Destroy (hit.transform.gameObject);
    
    				for(int x = -1; x <= 1; x++)
    					for(int y = -1; y <=1; y++)
    						for(int z = -1; z <= 1; z++)
    						{
    							if(!(x == 0 && y == 0 && z == 0))
    							{
    								Vector3 neighbour = new Vector3(blockPos.x+x, blockPos.y+y, blockPos.z+z);
    								DrawBlock(neighbour);
    							}
    						}
    			}
    		}
    	}
    
    }

Use the double equal sign ==