# ~/

## Brandon Rozek PhD Student @ RPI studying Automated Reasoning in AI and Linux Enthusiast.

# Lecture for October 23

## Two-Dimensional Arrays

You can think of a two dimensional array as a grid that is organized by rows then columns.

To declare a two dimensional array do the following

``````int[][] grid  = new int;  // Declares a 2D array of 5 rows and 5 columns
``````

You can have as many dimensions as you want. For graphics a 3-dimensional array would render 3D points.

It doesn’t have to be inherently visual though, you can have the n-dimensional array look at the interaction between n different variables. For example, the relationships to different questions in a survey.

Strings are essentially a char array with extra methods attached. We can imitate an array of strings with a 2D char array.

``````char[][] helloWorld = new char;
hello = 'h';
hello = 'e';
hello = 'l';
hello = 'l';
hello = 'o';
hello = 'w';
hello = 'o';
hello = 'r';
hello = 'l';
hello = 'd';
``````

## Nested-For Loops

To access the elements in a 2D array, you need to use a nested for-loop.

Here is how you print out the hello world example above

``````for (int row = 0; row < helloWorld.length; row++) {
for (int col = 0; col < helloWorld[row].length; col++) {
System.out.print(helloWorld[row][col]);
}
System.out.print(" ")
}
``````

The code above prints out “hello world”

## 2D Arrays in methods

You can write a get like method in the following way

``````public static void get(int[][] array, int row, int col) {
return array[row][col];
}
``````

Arrays in Java are pass by reference not pass by value. Meaning that if you change the array within the method then it will change outside the method.

``````public static void insert(int[][] array, int row, int col, int numToInsert) {
array[row][col] = numToInsert;
}
``````

To make it not be able to change the array inside the method, use the keyword `const` inside the method header. To code below will throw a compiler error.

``````public static void insert(const int[][] array, int row, int col, int numToInsert) {
array[row][col] = numToInsert; // This line will throw an errror
}
``````