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# Java Program to check for Diagonal Matrix

#### Question:

Write a Program in Java to input a 2-D square matrix and check whether it is a Diagonal Matrix or not.

Diagonal Matrix : A diagonal matrix is a matrix (usually a square matrix) in which the entries outside the main diagonal (↘) are all zero. The diagonal entries themselves may or may not be zero (but all diagonal entries cannot be zero).

Example:

$\begin{bmatrix} 5 & 0 & 0 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 0 \\ 0 & 0 & 0 & 7 \end{bmatrix}$

#### Solution:

/**
* The class DiagonalMatrix inputs a Matrix and checks whether it is a diagonal matrix or not
* @author : www.guideforschool.com
* @Program Type : BlueJ Program - Java
*/

import java.util.*;
class DiagonalMatrix
{
public static void main(String args[])throws Exception
{
Scanner sc=new Scanner(System.in);
System.out.print("Enter the size of the matrix : ");
int m=sc.nextInt();
int A[][]=new int[m][m];

/* Inputting the matrix */
for(int i=0;i<m;i++)
{
for(int j=0;j<m;j++)
{
System.out.print("Enter an element : ");
A[i][j]=sc.nextInt();
}
}

/* Printing the matrix */
System.out.println("*************************");
System.out.println("The Matrix is : ");
for(int i=0;i<m;i++)
{
for(int j=0;j<m;j++)
{
System.out.print(A[i][j]+"\t");
}
System.out.println();
}
System.out.println("*************************");

int p=0, q=0;

for(int i=0;i<m;i++)
{
for(int j=0;j<m;j++)
{
if(i!=j && A[i][j]!=0) // Checking non-diagonal elements
{
p=1;
break;
}
if(i==j && A[i][j]==0) // Checking diagonal elements
{
q++;
}
}
}

if(p==0 && q<m)
System.out.println("The matrix is Diagonal");
else
System.out.println("The matrix is not Diagonal");
}
}

#### Output:

Enter the size of the matrix : 4
Enter an element : 5
Enter an element : 0
Enter an element : 0
Enter an element : 0
Enter an element : 0
Enter an element : 1
Enter an element : 0
Enter an element : 0
Enter an element : 0
Enter an element : 0
Enter an element : 0
Enter an element : 0
Enter an element : 0
Enter an element : 0
Enter an element : 0
Enter an element : 7
*************************
The Matrix is :
5 0 0 0
0 1 0 0
0 0 0 0
0 0 0 7
*************************
The matrix is Diagonal

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Solution of Program 2 of ISC 2017 Computer Science Paper 2 (Practical) Exam. Java program to input the answers of each participant row-wise and calculate their marks