Arrays — terminology, 1D/2D arrays, pseudocode, and processing

An array is a fixed-size, ordered collection of values that all have the same data type. Think of it as a row of lockers. Each locker has a number on its door, and you open a locker by its number.

Key terms:

• Index (subscript): the number used to pick out one element. In Scores[3], the index is 3.
• Element: one value stored in the array.
• Lower bound: the smallest valid index. It is written in the declaration.
• Upper bound: the largest valid index.

Example: DECLARE Scores : ARRAY[1:10] OF INTEGER

• Lower bound = 1, upper bound = 10, so there are 10 elements.
• Valid indices are 1, 2, 3, ..., 10.
• Scores[1] is the first element and Scores[10] is the last.
• Scores[11] does not exist. Using it is an error called "index out of bounds".

The lower bound does not have to be 1. ARRAY[5:9] is also legal, with indices 5 to 9. Most examples in this lesson start at 1.