Use one-dimensional and two-dimensional arrays and records to store collections of data, and access elements using indexes and field names.

What this dot point is asking

AQA wants you to use one-dimensional and two-dimensional arrays and records to store collections of data, and to access individual elements using an index or a field name.

One-dimensional arrays

For example scores <- [10, 25, 8]; then scores[0] is 10 and scores[2] is 8. The big advantage is that an array can be processed with a loop: instead of naming a hundred variables, you store a hundred values in one array and step through the indexes with a FOR loop. A five-element array has valid indexes 0 to 4, so the last index is always one less than the number of elements.

Two-dimensional arrays

A 2D array suits anything naturally grid-shaped: a noughts-and-crosses board, a seating plan, a timetable, or a spreadsheet of marks. Nested loops (a loop inside a loop) are the standard way to visit every cell, the outer loop stepping through rows and the inner loop through columns.

Records

For example a student record might have fields name (string), age (integer) and present (Boolean), accessed as student.name and student.age. The field names make the code self-documenting, because student.age is clearer than an array element student[1].

Arrays versus records

The key contrast is that an array holds values of the same type accessed by a numeric index, while a record holds related values that may be of different types accessed by a field name. Real programs often combine them, for example an array of student records.

Processing a two-dimensional array

A 2D array is visited with nested loops: an outer loop steps through the rows and an inner loop steps through the columns of each row. For a grid board with 3 rows and 3 columns, FOR row <- 0 TO 2 containing FOR col <- 0 TO 2 then OUTPUT board[row][col] will print every cell, row by row. This is how you total a table of marks, search a seating plan, or check a noughts-and-crosses board. The key is to keep clear which index is the row and which is the column, and to loop each from 0 to one less than the number of rows or columns.

Try this

Q1. State what an array index is. [1 mark]

• Cue. The position number of an element, used to access it, usually starting at 0.

Q2. Explain one difference between an array and a record. [2 marks]

• Cue. An array stores values of the same type accessed by index; a record stores related values of possibly different types accessed by field name.