2-D arrays · ⁨مصفوفات 2-D⁩

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

Two indexes: row, column

• Use G[row, column] to reach one cell.
• The first cell is G[1,1].

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

Nested FOR over a grid

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

DECLARE G : ARRAY[1:2, 1:3] OF INTEGER
DECLARE R, C : INTEGER
FOR R ← 1 TO 2
    FOR C ← 1 TO 3
        G[R, C] ← R * C
    NEXT C
NEXT R
FOR R ← 1 TO 2
    FOR C ← 1 TO 3
        OUTPUT G[R, C]
    NEXT C
NEXT R

Watch out

• The order is G[row, column] — row first, then column. NEXT R

Common mistakes

• A 2-D array is ARRAY[1:r, 1:c]; 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.