I'm trying to write a simple square matrix multiplication method using multidimensional arrays.
package matrixmultiplication;
import java.util.Scanner;
public class Matrixmultiplication
{
public static void main(String[] args)
{
Scanner scan = new Scanner(System.in);
int [][] a,b,c;
int size;
System.out.print("Enter the Size of the matrix :");
size = scan.nextInt();
a=b=c=new int[size][size];
System.out.println("Enter the elements of the First matrix");
for(int i=0;i<size;i++)
{
for(int j=0;j<size;j++)
{
System.out.print("Enter the element a[" + i +"]["+ j + "] : ");
a[i][j] = scan.nextInt();
}
}
System.out.println("Enter the elements of the Second matrix");
for(int i=0;i<size;i++)
{
for(int j=0;j<size;j++)
{
System.out.print("Enter the element b[" + i +"]["+ j + "] : ");
b[i][j] = scan.nextInt();
}
}
System.out.println("The Product of the two matrix is : ");
for(int i=0;i<size;i++)
{
for(int j=0;j<size;j++)
{
int sum = 0;
for(int k=0;k<size;k++)
{
sum +=(a[i][k] * b[k][j]);
}
c[i][j] = sum;
System.out.print(c[i][j] + "\t");
}
System.out.println();
}
}
}
When I run this program in Netbeans ,I get the following output:
Enter the Size of the matrix :2
Enter the elements of the First matrix
Enter the element a[0][0] : 1
Enter the element a[0][1] : 1
Enter the element a[1][0] : 1
Enter the element a[1][1] : 1
Enter the elements of the Second matrix
Enter the element b[0][0] : 1
Enter the element b[0][1] : 1
Enter the element b[1][0] : 1
Enter the element b[1][1] : 1
The Product of the two matrix is :
2 3
3 10
The Correct output of this program should be :
2 2
2 2
Can someone tell me what is wrong with this code.
The problem is here:
a=b=c=new int[size][size];
This creates just one array, and makes all of the variables point to it. So, updating the elements of c is also updating the elements of a and b.
Create 3 arrays instead:
a=new int[size][size];
b=new int[size][size];
c=new int[size][size];