Answer 1

Loop variable? Do you mean the number between the square brackets? Those are used to represent (counting from zero) the number of values it will hold.
For example:
int myArray[2] = {1, 5, 2}; // Arrays start counting from zero

If you're talking about looping through an array, you can do the following to get the length of the array:
myArray.length(); // Which is 2

EDIT:
Arrays don't have to be initialized with a number between brackets if you give it's value. For example:
int mySecondVar[] = {12, 234, 2, 5}; // Automatically assumes array size of 3
int myThirdVar[4]; // It knows the length, but hasn't been assigned a value. OKAY.
int myFourthVar[]; // Error!