We informally define the term "corresponding element" as follows: The first element in an array and the last element of the array are corresponding elements. Similarly, the second element and the element just before the last element are corresponding elements. The third element and the element just before the element just before the last element are corresponding elements -- and so on. Given an array a and a variable n that contains the number of elements in a , write an expression for the corresponding element of a[i] .