Matrix is lower triangular or not

Posted on Apr 26, 2020

C program to check if matrix is lower triangular or not.

A square matrix is called lower triangular if all the entries above the main diagonal are zero.

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

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

    if(flag == 0)
    {
        printf("\nMatrix is lower triangular");
    }
    else
    {
        printf("\nMatrix is not lower triangular");
    }
}

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);

    low_tri(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]  :2
Element [1][1]  :3
Element [1][2]  :0
Element [1][3]  :0
Element [2][0]  :4
Element [2][1]  :5
Element [2][2]  :6
Element [2][3]  :0
Element [3][0]  :7
Element [3][1]  :8
Element [3][2]  :9
Element [3][3]  :10

Matrix entered is
1       0       0       0
2       3       0       0
4       5       6       0
7       8       9       10

Matrix is lower triangular


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

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]  :2
Element [0][3]  :0
Element [1][0]  :3
Element [1][1]  :4
Element [1][2]  :0
Element [1][3]  :0
Element [2][0]  :5
Element [2][1]  :6
Element [2][2]  :7
Element [2][3]  :0
Element [3][0]  :8
Element [3][1]  :9
Element [3][2]  :10
Element [3][3]  :11

Matrix entered is
1       0       2       0
3       4       0       0
5       6       7       0
8       9       10      11

Matrix is not lower triangular