Multi-Dimentioned Arrays!!

Arrays can have more than one dimention. In fact, there is no reasonable limit to the number of dimentions an array can have. If a one dimentional array (the old kind) can be thought of as a list then a two dimentional array can be thought of as a grid, like a checkerboard or a spreadsheet.

Single Dimentional Array

Red

Green

Blue

Orange

Brown

Double Dimentional Array

Red	Green	Blue
Blue	Green	Brown
Orange	Violet	Green

To use a multi-dimentional array, you must do the same three steps as with all arrays.

Declare the array. This is just like a single dimentioned array, except you use as many pairs of '[]' as there are dimentions. For example,

int doubledim[][]; Color tripledim[][][];

Allocate space for the array. This is just like before, except that you must supply a size for every dimention. For example,
doubledim = new int[10][20]; tripledim = new Color[10][20][30];
Use the array. If there are several dimentions to an array, then you will probably need several nested for loops to use the array correctly.

The size of a multi-dimentioned array is the product of the size of each dimention multiplied together. For example, if the array has dimentions of size 10, 20, and 30 then the array has 600 elements!

Here are some sample algorithms:

Find the largest element of an array
max = num[0][0]; for(i = 0; i < SIZE1; i++) {       for(j = 0; j < SIZE2; j++) {            if (max < num[i][j]) {                  max = num[i][j];            }        } } Sum all elements of an array
sum = 0; for(i = 0; i < SIZE1; i++) {       for(j = 0; j < SIZE2; j++) {            sum+=num[i][j];        } }

Here is a program that puts up a grid of colors. Everywhere you click, the color changes. This lets you draw and figure you want.

import java.awt.*; public class grid extends java.applet.Applet {
        Color grid[][]; // the main gridarray
        int x, y;       // where they clicked
        int i,j;        // index for for loops
        public void init() {
                grid = new Color [20][20];
                for(i = 0; i < 20; i++ ) {
                        for(j = 0; j< 20; j++ ) {
                                grid[i][j] = Color.green;
                        }
                }
        }
        public void paint(Graphics q) {
                for(i = 0; i < 20; i++ ) {
                        for(j = 0; j< 20; j++ ) {
                                q.setColor(grid[i][j]);
                                q.fillRect(i*20,j*20,20,20);
                                q.setColor(Color.black);
                                if (grid[i][j] == Color.green) {
                                        q.drawString("G", i*20+10, j*20+10);
                                }
                                else {
                                        q.drawString("R", i*20+10, j*20+10);
                                }
                        }
                }
        }
        public boolean mouseDown(Event ignored, int mousex, int mousey) {
                x = mousex / 20;
                y = mousey / 20;
                if (grid[x][y] == Color.green) {
                        grid[x][y] = Color.red;
                }
                else {
                        grid[x][y] = Color.green;
                }
                repaint();
                return true;    // required for all boolean functions
        }
}