Introduction. Data in a table or a matrix can be represented using a two-dimensional array. For example:

Transcription

1 Chapter 7 MULTIDIMENSIONAL ARRAYS Lecture notes for computer programming 1 Faculty of Engineering and Information Technology Prepared by: Iyad Albayouk ١

2 Introduction Data in a table or a matrix can be represented using a two-dimensional array. For example: ٢

3 Two-Dimensional Array Basics Declaring Variables of Multidimensional Arrays and Creating Multidimensional Arrays int[][] matrix = new int[10][ ][10]; or int matrix[][] = new int[10][ ][10]; matrix[0][ ][0]] = 3; for (int i=0; i<matrix.length; i++) for (int j=0; j<matrix[i].length; j++) { matrix[i][j] = (int)(math.random()*1000); } ٣

4 Multidimensional Array Illustration matrix = new int[5][5]; matrix[2][1] = 7; int[][] array = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10, 11, 12} }; ٤

5 Declaring, Creating, and Initializing Using Shorthand Notations You can also use a shorthand notation to declare, create and initialize a twodimensional array. For example, ٥

6 Obtaining the Lengths of Two- Dimensional Arrays For example, suppose x = new int[3][4], x[0], x[1], and x[2] are one-dimensional arrays and each contains four elements, as shown in below Figure. x.length is 3, and x[0].length, x[1].length, and x[2].length are 4. A two-dimensional array is a one-dimensional array in which each element is another one-dimensional array. ٦

7 Ragged Arrays Each row in a two-dimensional array is itself an array. So, the rows can have different lengths. Such an array is known as a ragged array. For example: As you can see, trianglearray[0].length is 5, trianglearray[1].length is 4, trianglearray[2].length is 3, trianglearray[3].length is 2, and triangle- Array[4].length is 1. ٧

8 Ragged Arrays, cont. The same as before - you can create a ragged array using the following syntax: int[ ][ ] trianglearray = new int [5][ ]; trianglearray[0] = new int[5]; trianglearray[1] = new int[4]; trianglearray[2] = new int[3]; trianglearray[3] = new int[2]; trianglearray[4] = new int[1]; The syntax new int[5][ ] for creating an array requires the first index to be specified. The syntax new int[ ][ ] would be wrong. ٨

9 Processing Two-Dimensional Arrays Suppose an array matrix is created as follows: int[ ][ ] matrix = new int[10][ ][10]; The following loop initializes the array with user input values: ٩

10 Processing Two-Dimensional Arrays, cont. The following loop initializes the array with random values between 0 and 99: ١٠

11 Processing Two-Dimensional Arrays, cont. Printing arrays. To print a two-dimensional array, you have to print each element in the array using a loop like the following: ١١

12 Processing Two-Dimensional Arrays, cont. The following loop for summing elements by column in array. ١٢

13 Passing Two-Dimensional Arrays to Methods import java.util.scanner; public class PassTwoDimensionalArray { public static void main(string[] args) { Int [ ][ ] m = getarray(); // Get an array System.out.println("\nSum of all elements is " + sum(m)); // Display sum of elements } public static int [ ][ ] getarray() { Scanner input = new Scanner(System.in); // Create a Scanner Int [ ][ ] m = new int[3][4]; System.out.println("Enter " + m.length + " rows and "+ m[0].length + " columns: "); for (int i = 0; i < m.length; i++) for (int j = 0; j < m[i].length; j++) m[i][j] = input.nextint(); return m; } public static int sum(int [ ][ ] m) { int total = 0; for (int row = 0; row < m.length; row++) { for (int column = 0; column < m[row].length; column++) { total += m[row][column]; } } return total; } } ١٣

14 Passing Two-Dimensional Arrays to Methods, cont. ١٤