C program to find lower triangular matrix

Write a C program to read elements in a matrix and check whether the matrix is a lower triangular matrix or not. C program to find whether the matrix is lower triangular or not. Logic to find lower triangular matrix in C programming.

Example

Input

Input elements in matrix:
1 0 0
4 5 0
7 8 9

Output

Matrix is lower triangular

Required knowledge

Basic C programming, For loop, Array

Lower triangular matrix

Lower triangular matrix is a special square matrix whose all elements above the main diagonal is zero.

Lower triangular matrix

Read more - Program to find upper triangular matrix

Logic to find lower triangular matrix

To find whether a matrix is lower triangular or not we need to check if all elements above main diagonal of the matrix is zero or not.
For any matrix A if elements Aij = 0 (Where j ≥ i). Means, if(array[row][col] == 0) and j > i then it is lower triangular matrix.

Program to find lower triangular matrix

/**
 * C program to find lower triangular matrix
 */

#include <stdio.h>
#define MAX_ROWS 3
#define MAX_COLS 3

int main()
{
    int array[MAX_ROWS][MAX_COLS];
    int row, col, isLower;

    /* Input elements in matrix from user */
    printf("Enter elements in matrix of size %dx%d: \n", MAX_ROWS, MAX_COLS);
    for(row=0; row<MAX_ROWS; row++)
    {
        for(col=0; col<MAX_COLS; col++)
        {
            scanf("%d", &array[row][col]);
        }
    }

    /* Check whether the matrix is lower triangular matrix */
    isLower = 1;
    for(row=0; row<MAX_ROWS; row++)
    {
        for(col=0; col<MAX_COLS; col++)
        {
            /*
             * If elements above main diagonal(col>row)
             * is not equal to zero(array[row][col]!=0)
             */
            if(col>row && array[row][col]!=0)
            {
                isLower = 0;
            }
        }
    }

    /*
     * If matrix is lower triangular matrix
     */
    if(isLower == 1)
    {
        printf("\nMatrix is Lower triangular matrix: \n");

        /* Print elements of lower triangular matrix */
        for(row=0; row<MAX_ROWS; row++)
        {
            for(col=0; col<MAX_COLS; col++)
            {
                printf("%d ", array[row][col]);
            }

            printf("\n");
        }
    }
    else
    {
        printf("\nMatrix is not a Lower triangular matrix");
    }

    return 0;
}

Output

Enter elements in matrix of size 3x3:
1 0 0
4 5 0
7 8 9

Matrix is Lower triangular matrix:
1 0 0
4 5 0
7 8 9

Happy coding 😉

About Pankaj

Pankaj Prakash is the founder, editor and blogger at Codeforwin. He loves to learn new techs and write programming articles especially for beginners. He works at Vasudhaika Software Sols as a Software Design Engineer and manages Codeforwin. In short Pankaj is Web developer, Blogger, Learner, Tech and Music lover.

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