c# create array

// Define and Initialize
int[] arr = {1, 2, 3};

// Buuuut:
// Initial defining
int[] arr;

// This works
arr = new int[] {1, 2, 3};   

// This will cause an error
// arr = {1, 2, 3}; 

int[] arr = Enumerable.Range(0, X+1).ToArray();