Define a one-dimensional array.

It is an ordered set of elements, all of the same data type, held under a single identifier and reached individually by an index.

What must be stated when an array is declared?

Its identifier, the data type of its elements, and how many elements it holds or the range of index values allowed.

How is a single element of an array referred to?

By writing the array's identifier followed by the index in brackets, as in marks[3].

What is the lower bound of an array, and why must a programmer know it?

It is the index of the very first element, which is 0 in some languages and 1 in others, and getting it wrong makes every later index one place out.

What is an out-of-bounds error?

It is an attempt to use an index outside the declared range, which either stops the program with an error or reads and writes memory that does not belong to the array.

WJEC A-Level Computer Science 601-5345-3

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Data Structures

One-dimensional arrays

3 things to know
AS Unit 1

Overview

One-dimensional array, lower bound of an array and out-of-bounds error.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

An array of ten elements has a lower bound of 0. What is the last valid index?

Key term

Why does reaching any element of an array take the same amount of work?

Key term

State the calculation that gives the address of element i of an array.

Questions from this subtopic

Each one with the model answer underneath.

1
Define a one-dimensional array.
Model answer
It is an ordered set of elements, all of the same data type, held under a single identifier and reached individually by an index.
2
What must be stated when an array is declared?
Model answer
Its identifier, the data type of its elements, and how many elements it holds or the range of index values allowed.
3
How is a single element of an array referred to?
Model answer
By writing the array's identifier followed by the index in brackets, as in marks[3].
4
What is the lower bound of an array, and why must a programmer know it?
Model answer
It is the index of the very first element, which is 0 in some languages and 1 in others, and getting it wrong makes every later index one place out.
5
An array of ten elements has a lower bound of 0. What is the last valid index?
Model answer
The last valid index is 9, because ten consecutive positions starting at 0 end at 9.
6
What is an out-of-bounds error?
Model answer
It is an attempt to use an index outside the declared range, which either stops the program with an error or reads and writes memory that does not belong to the array.

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