Transcript Multidimensional Arrays 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.

Multidimensional Arrays
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);
}
Multidimensional Array Illustration
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matrix = new int[5][5];
7
matrix[2][1] = 7;
3
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int[][] array = {
{1, 2, 3},
{4, 5, 6},
{7, 8, 9},
{10, 11, 12}
};
Declaring, Creating, and Initializing Using
Shorthand Notations
You can also use a shorthand notation to declare, create and
initialize a two-dimensional array. For example,
int[][] array = {
{1, 2, 3},
{4, 5, 6},
{7, 8, 9},
{10, 11, 12}
};
This is equivalent to the following statements:
int[][] array
array[0][0] =
array[1][0] =
array[2][0] =
array[3][0] =
= new int[4][3];
1; array[0][1] = 2; array[0][2] =
4; array[1][1] = 5; array[1][2] =
7; array[2][1] = 8; array[2][2] =
10; array[3][1] = 11; array[3][2]
3;
6;
9;
= 12;
Lengths of Multidimensional
Arrays
int[][] array = {
{1, 2, 3},
{4, 5, 6},
{7, 8, 9},
{10, 11, 12}
};
array.length
array[0].length
array[1].length
array[2].length
array[3].length
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,
int[][] matrix = {
{1, 2, 3, 4, 5},
{2, 3, 4, 5},
{3, 4, 5},
{4, 5},
{5}
};
Example 5.7
Adding and Multiplying Two Matrices
 Objective:
Use two-dimensional arrays to
create two matrices, and then add and multiply
the two matrices.
 a11 a12 a13 a14 a15 
 b11 b12 b13 b14 b15 
 a11  b11





a
21 a 22 a 23 a 24 a 25
b
21 b 22 b 23 b 24 b 25




 a 21  b21
 a 31 a 32 a 33 a 34 a 35    b31 b32 b33 b34 b35    a 31  b31





 a 41 a 42 a 43 a 44 a 45 
 b41 b42 b43 b44 b45 
 a 41  b41
 a 51 a 52 a 53 a 54 a 55 
 b51 b52 b53 b54 b55 
 a 51  b51





a12  b12 a13  b13 a14  b14 a15  b15 

a 22  b22 a 23  b23 a 24  b24 a 25  b25 
a 32  b32 a 33  b33 a 34  b34 a 35  b35 

a 42  b42 a 43  b43 a 44  b44 a 45  b45 
a 52  b52 a 53  b53 a 54  b54 a 55  b55 
TestMatrixOperation
Run
Example 5.7 (cont) Adding and
Multiplying Two Matrices
 a11 a12 a13 a14 a15 
 b11 b12 b13 b14 b15 
 c11 c12 c13 c14 c15 






 a 21 a 22 a 23 a 24 a 25 
 b21 b22 b23 b24 b25 
 c 21 c 22 c 23 c 24 c 25 
 a 31 a 32 a 33 a 34 a 35    b31 b32 b33 b34 b35    c 31 c 32 c 33 c 34 c 35 






 a 41 a 42 a 43 a 44 a 45 
 b41 b42 b43 b44 b45 
 c 41 c 42 c 43 c 44 c 45 
 a 51 a 52 a 53 a 54 a 55 
 b51 b52 b53 b54 b55 
 c 51 c 52 c 53 c 54 c 55 






cij = ai1b1j+ai2b2j+ai3b3j+ai4b4j+ai5b5j
Example 5.8
Grading Multiple-Choice Test

Students’ Answers to the Questions:
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Student
Student
Student
Student
Student
Student
Student
Student
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1
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7
A
D
E
C
A
B
B
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B
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D
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B
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B
A
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D
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C
D
A
B
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E
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A
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A
A
A
A
A
A
D
D
D
D
D
D
D
D
Objective: write a
program that grades
multiple-choice test.
Key to the Questions:
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Key
D B D C C D A E A D
Grade Exam
Run