One-dimensional and two-dimensional arrays

One-dimensional arrays

An array stores many values of the same data type under one name. Each value is an element, found by its index in square brackets. Declare the lowest and highest index when you create the array.

DECLARE Scores : ARRAY[1:6] OF INTEGER
Scores[1] <- 72
Scores[3] <- 88
OUTPUT Scores[3]

Arrays and loops

Arrays and FOR loops belong together: the loop counter becomes the index, so the same code processes every element.

DECLARE Scores : ARRAY[1:6] OF INTEGER
DECLARE Index : INTEGER
DECLARE Total : INTEGER
Total <- 0
FOR Index <- 1 TO 6
    INPUT Scores[Index]
    Total <- Total + Scores[Index]
NEXT Index
OUTPUT "Average: ", Total / 6

Two-dimensional arrays

A 2D array is a table with rows and columns. It needs two indexes: the row first, then the column. Click any cell below.

Nested loops for 2D arrays

To visit every element, use one loop for the rows and another inside it for the columns.

DECLARE Marks : ARRAY[1:3, 1:4] OF INTEGER
DECLARE Student : INTEGER
DECLARE Test : INTEGER
DECLARE Total : INTEGER
FOR Student <- 1 TO 3
    FOR Test <- 1 TO 4
        INPUT Marks[Student, Test]
    NEXT Test
NEXT Student
FOR Student <- 1 TO 3
    Total <- 0
    FOR Test <- 1 TO 4
        Total <- Total + Marks[Student, Test]
    NEXT Test
    OUTPUT "Student ", Student, " total: ", Total
NEXT Student

Key terms

Array

A data structure holding many values of the same type under one identifier.

Element

One value stored in an array.

Index

The position number used to access an element.

2D array

An array with rows and columns, accessed with two indexes.

Check yourself