int pop(int a[], int& n) {
// function:
// Reads from cin until array full or to an EOF.
// parameters:
// a in array of values.
// n inout number of values in a, a[0]..a[n-1]
// returns:
// value that was at the end (top) of the array values.
if (n <= 0) {
;// ERROR - return special value, halt, throw exception, or expand array.
}
n--;
return a[n];
}