2-D arrays

A 2-D array is a grid

• A 2-D array has rows and columns, like a table.
• ARRAY[1:2, 1:3] means 2 rows and 3 columns.

DECLARE Grid : ARRAY[1:2, 1:3] OF INTEGER
Grid[1,1] ← 5
OUTPUT Grid[1,1]     // → 5

Two indexes: row, column

• Use Grid[Row, Column] to reach one cell.
• The first cell is Grid[1,1].

DECLARE Grid : ARRAY[1:2, 1:2] OF INTEGER
Grid[1,2] ← 7
Grid[2,1] ← 9
OUTPUT Grid[1,2]     // → 7

Nested FOR over a grid

• An outer loop walks the rows; an inner loop walks the columns.

DECLARE Grid : ARRAY[1:2, 1:3] OF INTEGER
DECLARE Row, Column : INTEGER
FOR Row ← 1 TO 2
    FOR Column ← 1 TO 3
        Grid[Row, Column] ← Row * Column
    NEXT Column
NEXT Row
FOR Row ← 1 TO 2
    FOR Column ← 1 TO 3
        OUTPUT Grid[Row, Column]
    NEXT Column
NEXT Row

Watch out

• The order is Grid[Row, Column] — row first, then column.

Common mistakes

• A 2-D array is ARRAY[1:RowCount, 1:ColumnCount]; use two indexes.
• The outer loop walks the rows, the inner the columns.

Now you try

• Use two indexes, or nested FOR loops.
• Press Check answer to test it.