Arrays are containers for data sets of the same type. Of course, the container has a standard size. How many elements can an array store? Its subscript starts counting from 0, which is not in line with the daily habit of counting from 1 When the subscript exceeds the number of elements in the array minus 1, the array overflows. Computers use virtual memory to manage physical memory. An address maps to a piece of memory. It is illegal to index unmapped memory, and a segment error will occur! The number sequence in mathematics is a series of regular numbers, so don't confuse the concepts. Since learning computer, we should treat computer problems according to the scientific terms of computer, and don't just find a mathematical concept and ignore it.