Matrix is identity matrix or not

Posted on Apr 26, 2020

C program to check if a matrix is identity matrix or not.

Identity matrix of size n is the n × n square matrix in which elements of principle (main) diagonal are ones, and the rest of the elements are zeroes. Identity matrix is also known as unit matrix.

Program

#include<stdio.h>
#include<conio.h>
#define MAX 10

void read_matrix(int mat[MAX][MAX], int row, int col)
{
    int i, j;
    for(i=0;i<row;i++)
    {
        for(j=0;j<col;j++)
        {
            printf("Element [%d][%d]\t:",i,j);
            scanf("%d",&mat[i][j]);
        }
    }
}

void print_matrix(int mat[MAX][MAX], int row, int col)
{
    int i, j;
    for(i=0;i<row;i++)
    {
        for(j=0;j<col;j++)
        {
            printf("%d\t",mat[i][j]);
        }
        printf("\n");
    }
}

void identity(int mat[MAX][MAX], int row)
{
    int i, j, flag;

    flag = 0;
    for(i=0;i<row;i++)
    {
        for(j=0;j<row;j++)
        {
            if((i==j) && mat[i][j]!=1)
            {
                flag = 1;
            }
            else if(i!=j && mat[i][j]!=0)
            {
                flag = 1;
            }

        }
    }

    if(flag == 0)
    {
        printf("\nMatrix is identity matrix");
    }
    else
    {
        printf("\nMatrix is not an identity matrix");
    }
}

void main()
{
    int mat[MAX][MAX];
    int row, col;

    printf("Enter the number of rows or columns of the square matrix\t:");
    scanf("%d",&row);
    col = row;

    printf("Enter the elements of the matrix\n");
    read_matrix(mat, row, col);

    printf("\nMatrix entered is\n");
    print_matrix(mat, row, col);

    identity(mat, row);

    getch();
}

Output

********** Run1 ********** 

Enter the number of rows or columns of the square matrix        :4
Enter the elements of the matrix
Element [0][0]  :1
Element [0][1]  :0
Element [0][2]  :0
Element [0][3]  :0
Element [1][0]  :0
Element [1][1]  :1
Element [1][2]  :0
Element [1][3]  :0
Element [2][0]  :0
Element [2][1]  :0
Element [2][2]  :1
Element [2][3]  :0
Element [3][0]  :0
Element [3][1]  :0
Element [3][2]  :0
Element [3][3]  :1

Matrix entered is
1       0       0       0
0       1       0       0
0       0       1       0
0       0       0       1

Matrix is identity matrix


********** Run2 ********** 

Enter the number of rows or columns of the square matrix        :3
Enter the elements of the matrix
Element [0][0]  :1
Element [0][1]  :0
Element [0][2]  :4
Element [1][0]  :0
Element [1][1]  :1
Element [1][2]  :0
Element [2][0]  :0
Element [2][1]  :0
Element [2][2]  :1

Matrix entered is
1       0       4
0       1       0
0       0       1

Matrix is not an identity matrix