Can't input value into for loop ,Can't set values in for loop

Hello, I have a problem with my for loop :

GameObject[] x;
Transform[] y;
Rigidbody rigidbody;

for (int i; i < x.Length; i++)

The vector is a property of x. Unity refuses to recognize x and y inside the loop, even though I have already defined them.
What do ?

@sam_fechier you have to initialize the array first before you can access or assign the elements: GameObject[] x = new GameObject[LengthHere]; and same with the other array: Transform[] y = new Transform[SomeLength];