how can i check if index exists?

I am trying to check if there is an object to any side of it in the 3d array. My function to check is :

void UpdateSides ()
	{
		Vector3 myPos = transform.position;
		int x = (int) myPos.x;
		int y = (int) myPos.y;
		int z = (int) myPos.z;
		
		if (levelData[x, y, z] != null)
		{
			if ( x < levelData.GetLength(0) && y < levelData.GetLength(1) && z < levelData.GetLength(2))
			{
				print ("Pass GetLength Test");
				if (x-1>-1 && y-1>-1 && z-1>-1)
				{
					print ("Pass Over 0");
					
					if (levelData[x, y+1, z] == null)
					{
						print ("Nothing Above");
					}
					if (levelData[x, y+1, z] != null)
					{
						print ("Something Above");
					}
					if (levelData[x, y-1, z] == null)
					{
						print ("Nothing Below");
					}
					if (levelData[x, y-1, z] != null)
					{
						print ("Something Below");
					}
					if (levelData[x+1, y, z] == null)
					{
						print ("Nothing Right");
					}
					if (levelData[x+1, y, z] != null)
					{
						print ("Something Right");
					}
					if (levelData[x-1, y, z] == null)
					{
						print ("Nothing Left");
					}
					if (levelData[x-1, y, z] != null)
					{
						print ("Something Left");
					}
					if (levelData[x, y, z+1] == null)
					{
						print ("Nothing Forward");
					}
					if (levelData[x, y, z+1] != null)
					{
						print ("Something Forward");
					}
					if (levelData[x, y, z-1] == null)
					{
						print ("Nothing Back");
					}
					if (levelData[x, y, z-1] != null)
					{
						print ("Something Back");
					}
				}
			}
		}
	}

I have been trying to figure out what i am doing wrong and i just cant seem to find it. Im trying everything. Im using one of the lines that was recommended and now it still isnt working.

Try this:

if ( x < levelData.GetLength(0)
  && y < levelData.GetLength(1)
  && z < levelData.GetLength(2))
{
    //your code
}

Thank you ahmedbenlakhdhar. I used your code. The only thing i had to fix was that i put a -1 at the end to get one shorter of the length. The code i used is:

void UpdateSides ()
	{
		Vector3 myPos = transform.position;
		int x = (int) myPos.x;
		int y = (int) myPos.y;
		int z = (int) myPos.z;
		
		if (levelData[x, y, z] != null)
		{
			if (x < levelData.GetLength(0)-1)
			{
				if (x-1>-1)
				{
					if (levelData[x+1, y, z] == null)
					{
						print ("Nothing Right");
					}
					if (levelData[x+1, y, z] != null)
					{
						print ("Something Right");
					}
					if (levelData[x-1, y, z] == null)
					{
						print ("Nothing Left");
					}
					if (levelData[x-1, y, z] != null)
					{
						print ("Something Left");
					}
				}
			}
			if (y < levelData.GetLength(1)-1)
			{
				if (y-1>-1)
				{
					if (levelData[x, y+1, z] == null)
					{
						print ("Nothing Above");
					}
					if (levelData[x, y+1, z] != null)
					{
						print ("Something Above");
					}
					if (levelData[x, y-1, z] == null)
					{
						print ("Nothing Below");
					}
					if (levelData[x, y-1, z] != null)
					{
						print ("Something Below");
					}
				}
			}
			if (z < levelData.GetLength(2)-1)
			{
				if (z-1>-1)
				{
					if (levelData[x, y, z+1] == null)
					{
						print ("Nothing Forward");
					}
					if (levelData[x, y, z+1] != null)
					{
						print ("Something Forward");
					}
					if (levelData[x, y, z-1] == null)
					{
						print ("Nothing Back");
					}
					if (levelData[x, y, z-1] != null)
					{
						print ("Something Back");
					}
				}
			}
		}
	}